Z-100 Floppy Drives

Since the first single side, single density (SSSD), 8" floppy drives were placed in service for the early computers in the late 1970s, there have been several advancements developed:

  • Single Side, Single Density (SSSD), 48tpi 5.25"
  • Double Side, Double Density (DSDD), 48tpi 5.25"
  • Double Side, High Density (DSHD), 96tpi 5.25"
  • Double Side, Double Density (DSDD), 67tpi 3.5"
  • Double Side, High Density (DSHD), 135tpi 3.5"
  • 2" microfloppy, and others, including optical drives.

This article will concentrate on the most popular floppy drives used in the Z-100 computer series.

Note:  For easier reading and simplicity, I’m going to refer to the drives and disks as 8", 5" and 3", omitting the decimals. I’m also going to refer to the Z-DOS operating system and monitor ROM (ZROM) versions as v2, v3, and v4, again dropping the decimal intermediate versions.


          Z110PIC          Z120PIC

                            Z-110 Low-Profile                                                               Z-120 All-In-One


While the first floppy drives found within the Z-100 were the 5", 48tpi, single side, single density (SSSD), full height drives, like those shown here, within a short period, the most popular configuration of drives marketed in the Z-100 was a pair of double side, double density (DSDD) half height 5" drives or a single DSDD half height 5" drive with a “Winchester” 10Mb hard drive.

The 50-pin connector on the Z-207 Floppy Controller could also accommodate an external 8" drive.

The standard Z-100 Floppy Disk Controller could use up to four single or double density drives on the 34-pin connector and another four high density drives on the 50-pin connector. The Z-100 series computer could also use two floppy controllers, for up to 16 floppy drives!

However, the software of the period, Z-DOS and CP/M could only accommodate a limited number of drives at a time. As a default, the drive letters, A: and B: were assigned to the standard 5" floppy drives. The drive letters, C: and D: were assigned to the 8" variety of drives on the 50-pin connector. And the drive letters, E: through H: were assigned to any hard drive partitions, if installed.

In order to use other drives, the drive letters would have to be reassigned, using the ASSIGN command.

Note:  With Z-DOS v4, the drive letters A: through Z: could be assigned as desired through the DRIVECFG utility.

All in all, the Z-100 series computer was very flexible when it came to the use of floppy disk drives.

Note:  In 1989 William E. Flanagin developed DiskPack, a Floppy Disk Device Driver for the Z-100 computer that changed everything. It was a software package, marketed by Paul Herman, which allowed the use of all popular 8", 5", and 3" floppy disk formats, including many strange formats used by other computer systems, and PC-compatible formats. Email “Z-100 LifeLine” for additional information.

For more information with drive specifics, such as setup and configuration, please refer to my article: Z-100 Floppy Drives.



Z-100 Hard Drives

Since the first 5, 10, or 12Mb hard drives (called Winchester Drives by Zenith) were placed in the Z-100 in the mid-80s, there have been several more advanced types developed - MFM, RLL, SCSI, IDE and others. The drives usually found in the Z-100 were the first type - MFM - and the subject of this article.

Another drive type - SCSI - with considerably larger capacities, became available for the Z-100 in the late 80s with a SCSI Controller marketed by C.D.R. Paul Herman, editor and publisher of the “Z-100 LifeLine” at the time tried to get a special order of boards from C.D.R. adapted specifically for the Z-100. However, it soon became evident to Paul, and several volunteers working as his staff, that they needed to develop their own controller, and the new Z-100 LifeLine SCSI/EEPROM board was created.

As the MFM and newer SCSI systems became more scarce, attention turned to the newer IDE technology and another group of volunteers; John Beyers, Charles Hett, and I. We researched and developed the new Z-100 LifeLine IDE NvsRAM board, shipped in late 2008.

You can find additional information on these newer systems elsewhere on this site. This article will concentrate on the use of the initial Winchester hard drive.

The Heathkit/Zenith MFM hard drive installation was comprised of a Z-217 Winchester Controller Card in the card cage, a separate, unique Data Separator Board that was normally mounted near or over the hard drive and the MFM hard drive itself. These pictures show the drive configuration possible for the Z-120 All-In-One Computer:


   Z120DriveBay3a      Z120DriveBay4a


Note:  For full procedures on installing an MFM Hard Drive in the Z-100 series computer, please see the article, MFM Hard Drive Installation.


Preparing the Hard Drive



IMPORTANT: Early MFM hard drives are fragile and can be damaged easily. In all hard drives, while the drive’s platter is spinning, the read/write heads float on a very thin layer of air, separ-ating the heads from the platter’s surface. However, the read/write heads on these early drives came to rest on the surface of the disk platter when rotation stopped. Any bumping, knocking, or dropping may cause the heads to bang against the surface of the platter. A severe bump, especially while the platter is spinning, could actually damage or gouge out a small area in the platter and cause a “crash”, where an important portion of a program is unreadable and lost because the disk surface was damaged. Further, the read/write head may also be damaged.



For early hard drives, it is CRITICAL to run a disk utility that parks the heads in an unused portion of the disk - a storage or parking area - before the heads come to rest. Such a utility is SHIP, an external command packaged in CP/M and MS-DOS operating systems. Later MFM drives had an auto-park feature that placed the heads down after the last usable sector of the drive, in an unused area. But even then, the heads could be damaged from a sudden drop of the drive.





MFM drives are recognized by their two ribbon cable card edge connectors, one with 34 conductors and the other with 20 conductors. RLL drives also have these but the drive model number includes an R. For example, an ST-138 is an MFM drive, while an ST-138R is an RLL drive, with different formatting, capacities, and controller boards. ESDI drives also have similar cable connections, but cannot be used.


MFM drives are becoming available from Ebay and the used market, sometimes at ridiculous prices and there is no guarantee that any of these will work.

But let’s assume that you find one with possibilities and want to try it. What is involved?



CAUTION: You cannot just slap an MFM drive from another computer into your Z-100 and expect it to work, without completely reformatting the drive. It will require low level formatting using the Z-100 PREP command, partitioning using the PART command, and a high level formatting of each partition using the FORMAT command. These commands are unique to the Heath/Zenith CP/M and MS-DOS (now referred to as Z-DOS) operating systems.

There are numerous manufacturers of MFM drives, each with different sets of programming plugs, jumpers, and terminating resistors. If you have a specific brand that you can’t figure out, try emailing me at the “Z-100 LifeLine”.

As I mentioned earlier, please refer to the MFM Hard Drive Installation, which was published in Issue #59, for the full procedures for installing a hard drive in the Z-100. Here are views of my hard drive setup on my test bed Z-100:


HDriveTest1     HDriveTest3     Note the Cabling.


However, there are a few specific reminders:

*  Try to install the new drive alone and boot to a floppy to run the Winchester Disk Utilities. It can be run from another hard drive, but you would hate to accidently PREP the wrong drive!

*  If the new drive is installed alone, insure the terminating resistor pack is installed. If it is the second drive, only install the terminator resistor on the hard drive installed last on the 34-pin connector ribbon.

*  Double check that the ribbon cables are installed per the directions in Issue #59. Insure all connectors are fully seated and that pin one of each ribbon connector (the ribbon cable may also have a red edge) is at the correct end of the connectors on the drive, controller, and data separator. The 20-pin cable connector can go to either location on the Data Separator Card.

*  Before running PREP on a hard drive, you must install the Format Enable Jumper on the Z-217 Controller Card. It is located under the power connector in the upper left corner of the Z-217 Hard Drive Controller, and may be stored anywhere along the top row of pins of the VI* jumpers, when not in use.

*  Check for a programming plug on the new drive before installation and make a note of the position of any jumpers. Try this setting first and if unsuccessful, try the other positions before giving up.

Hint:  Drive Select (DS) pins may be labeled DS0 through DS3 or DS1 through DS4, if labeled at all. If this is the lone drive, DS0 (or DS1) will become drive unit 0 and after programming, drive E:.

Hint:  Before changing any positions on the programming plug, install the hard drive temporarily, boot up the computer, and run ASGNPART 0:. If the drive is already setup as drive 0: the drive LED should light. If it does not, check ASGNPART 1: and even 2: and 3: before giving up. If the LED will not light in any position, check the cables for an improper connection and finally try a different position on the programming plug.

Note:  If partition info is displayed after running ASGNPART, do not proceed with PREP until you have tried other options. For example:

-  Try running ASGNPART X:(Partition name) E:, where X: is the drive unit number. Then do a directory listing on E:.

-  Try running DETECT or VERIFY to see how many bad sectors are found.

-  Try reformatting the partition with FORMAT to isolate those bad sectors.

The PREP and PART utilities were available on a special disk entitled ‘Winchester Utilities Disk’, distributed separately from the earlier MS-DOS versions. The disk and instructions are available from the Z-100 LifeLine Library.

CAUTION:  Using PREP is the last resort. It will destroy all the files that may exist on the hard drive. If the disk is from another Z-100, you may need to use PREP only if you consistently encounter an unreasonable number of disk access errors. Do NOT use PREP until you have backed up all important files you wish to keep to floppy disks.

PREP has been updated by John Beyers in the Z-100's Z-DOS v4 that allows it to be much more flexible in its operation - another reason to upgrade.

All versions of the PREP utility enable you to:

*  Initialize the surface of the hard disk.

*  Test the data retention capabilities of the hard disk.

*  Isolate questionable disk sectors.

*  Divide the surface of the hard disk into 2 partitions (Z-DOS and CP/M).

PREP takes a long time to run. Expect it to take about 1.5 hours for every 10 megabytes in hard drive size. It runs seven surface passes. However, with the version 4 PREP, you can set the number of passes to make.

If the hard disk does not contain initialization information (from a prior PREP operation), PREP will prompt you to enter characteristics (in hex) in order to identify the type of hard drive that is being installed in the computer. While Issue #59 has a list of common drives that were used in the Z-100, I have updated this information for many more manufacturers. Please see the PDF document: Hard Drive Specs.

Note:  Several of the drives are too large for normal use in the Z-100. Early hard drives and Z-DOS versions in the Z-100 were limited to 32Mb. Later, with the addition of the PREP /k switch (which uses 1024 byte sectors rather than 512 byte sectors), the limit was extended to 64Mb. As I understand it, Z-DOS version 4 can go higher, though I don’t recall the limit. Just remember, larger than 64Mb will ONLY work with Z-DOS v4. The fix is easy - just reduce the number of heads being used by PREP until the number of megabytes is where you want it.

Once PREP has completed, if you run ASGNPART 0: you will see the two partitions created: Z-DOS and CP/M. If you are satisfied with these two partitions, you will not need to repartition the disk with PART. However, if you wish to change this partition information, you must run the PART utility.

The PART utility is self explanatory. Just follow the procedures as given to change the partition names and sizes as necessary, then choose a default boot partition and save the configuration to the hard drive. When complete, you may need to reboot the computer to the floppy drive again.

Next run ASGNPART 0: to confirm the partitions are as you required.

Before we can use the new partitions, you need to assign drive letters to them and then run FORMAT to do a high level format of each new partition. Run ASGNPART 0:(partition name) E: to assign the drive letter E: to the first partition. Likewise, assign succeeding drive letters (F:, G:, H:) to the remaining new partitions (up to four at a time). Run FORMAT X:/s/v to format and load the system files on each new partition, where X: can be E:, F:, G:, or H:.

If successful, you are now in business. Email me if you have any difficulty. I hope this helps clarify the use of Z-100 MFM hard drives.


H/Z-100 Seagate MFM Hard Drive Repair

General Notes:

  • Many, many years ago, I had run across an article in one of the computer magazines serving Heath/Zenith computer users; REMark, Sextant, or Capital HUG (CHUG), that reported that the H/Z-100 had poor regulation in its power supply and suggested adding a 47uF capacitor to the +5Vdc line of each hard drive.
  • This rather unalarming message has increased in importance over the last few years because of the aging hard drives being used in the H/Z-100.
  • The number of Seagate hard drives with no-spin problems has increased dramatically over recent years.
  • Many articles in various magazines have been attributing this problem to STICTION - the drive heads sticking to the very smooth, polished surface of the drive platters, which become even more polished with age/use.

WARNING:  The following fix requires some knowledge of electronics and soldering skills! Try this only on otherwise unusable hard drives and ONLY AT YOUR OWN RISK!


Possible Solution to Stiction Symptoms:

Over several years of experimentation, I had found that the poor power supply regulation and the stiction problem seemed to be RELATED! Further, if you touch a 5 volt jumper lead to a couple of pins (I forget which ones now) on the controller chip of the drive's attached controller board, the drive will indeed spin! This is NOT stiction, but a board issue.

I've now played with more than 10 drives, mostly ST-251s and ST-138's that wouldn't spin. Of these, several were repaired by replacing the 22uf surface mounted capacitor on the +5Vdc line with 47uf electrolytic capacitors. On the two other drives, the heads were so stuck, that turning the platters by hand broke off one of the heads on each! (Now, that's STICTION!).

Before throwing away any old drive that does not want to spin any more, if you are knowledgeable with soldering and want to try to salvage your drive, try replacing this capacitor. For the +5Vdc line, I recommend a 10v or 16v, 47uF electrolytic capacitor with the two leads out the same end. If you want to also replace the +12v capacitor (I believe it improves read/write reliability), try finding a small 25v, 47uF capacitor, no bigger than 1/4" in diameter. They can be found at most electronics stores.

While there have been numerous models of controller boards on the ST-138 and ST-251 drives, generally the correct capacitor is easy enough to locate as they are always located next to the power supply connector. Check which colored lead is the 5Vdc line from the computer power supply (red on the Z-100) and using an ohmmeter, locate the positive lead of the nearest 22uF capacitor connected to that connector. Fold the negative lead of the capacitor back along the side of its case and solder the leads to the vacant pads of the removed capacitor. The capacitor should lay on its side against the board. The positive lead MUST go to the pad connected to the 5Vdc line, generally marked with a plus (+) sign, and the negative lead MUST go to the pad connected to ground.

This fix may be applicable to other computers and Seagate drives. You'll find that some other drive manufacturers already use 47uF capacitors.


Beginner's Guide to the Z-100

Z110PIC      Z120PIC

The Z-110 Low-Profile Computer                                       The Z-120 All-In-One Computer


This article is an update to one written by Paul F. Herman that he originally published in the October 1991 edition of the "Z-100 LifeLine", issue #16. This version was published in issue #108, of November-December 2006. It has been updated to provide information on the newer developments that have been added over the years since that first article.

In This Guide...

I Just Bought a Z-100... Now What?

PC Compatibility

   -  Is the Z-100 a PC Compatible Computer?

   -  Can the Z-100 Run IBM-PC Software?

Operating Systems for the Z-100

   -  What Versions of DOS Does the Z-100 Use?

   -  Are Other Operating Systems Available?

About the Hardware

   -  What Do the Rear Panel Connectors Do?

   -  What Does DIP Switch S-101 do?

   -  What Kind of Printer Will Work?

   -  What Kind of Video Monitor Can I Use?

   -  Can I Add a Hard Disk to the Z-100?

   -  Can I Read/Write PC Compatible Disks?

Getting Started Without Documentation

   -  Power-Up Check

   -  How To Take Off The Cover

   -  The Hand Prompt

   -  System Information

Booting Up

   -  Configuration

   -  Accessing Already Bootable Hard Drive

   -  Accessing Hard Drive Partitions

Wrapping It Up

I Just Bought a Z-100... Now What?

This article is meant as a guide for anyone who has bought a used Z-100 for the first time. It could also be a refresher course to any of you who has forgotten some of this stuff and has attempted to turn on their Z-100 after along absence to find that it is inoperative. It will answer questions which are elementary for most of us, but which are of paramount importance to someone who has never seen, or heard of, a Z-100 computer before. The buyer of a used Z-100 is immediately at a disadvantage, because the machine may not come with the proper documentation, or software. In fact, it may not even work.

Hopefully, the answers can be found here.

Many used Z-100s are purchased from folks who are finally upgrading to bigger and better machines, or have finally decided to clean out the attic, garage, or basement and need to part with their long-unused treasures. Generally, in these cases the purchaser is in pretty good shape because the machine will come with a pile of software and technical literature accumulated by the first owner. And if there are any difficulties, the new owner can usually ask the seller for help.

But many used Z-100s being purchased are bought at an auction or surplus outlet for a price typically around $40. The buyers usually think that they are getting an IBM-PC compatible computer (aren't all computers IBM compatible?) and don't know what to do when it won't boot their borrowed copy of PC-DOS. A large number of Z-100s were also purchased at government auctions, sold to the highest bidder without any software - not even DOS.

Many of you who have read up to this point are beginning to say that this doesn't have anything to do with you, because you already have a Z-100, and you are not a novice. That may be true, but you should realize that these new Z-100 owners need our help to figure out how to use their new computers. And we need their continued support to extend the useful life of the Z-100. If a new user can't get his Z-100 working and doing useful things, he will throw it away and buy a PC clone instead. On the other hand, if we help him discover the capabilities of the Z-100, he will continue to use it and may contribute to the Z-100 community in the future. When you consider that tens of thousands of Z-100s were owned by the government and auctioned off, the level of help and support the new buyers receive may have a drastic affect on the future of the Z-100.

The "Z-100 LifeLine" has become the only clearing house left for Z-100 information, parts and service. Heath/Zenith and their Users' Group, and most other resources, have long packed up and gone, leaving us as the only means of help available. As Editor of the "Z-100 LifeLine", I'm committed to serving the Z-100 community for as long as I possibly can.

Let's begin with the more commonly asked questions and then finish by going through a step by step procedure to help you figure out if your Z-100 is operating properly, and to help you get your system on line - even if you may not have any documentation.

PC Compatibility

Is the Z-100 a PC Compatible Computer?

In a word, No. But before you get discouraged, some additional explanation is in order. When I say that the Z-100 is not IBM-PC compatible, this is to say that it will not run all of the software that you can buy for a PC clone. However, both the Z-100 and the IBM-PC of the time use the MS-DOS operating system, and the same CPU chip family, so many programs WILL run on both machines. These programs are generally referred to as "Generic DOS" programs.There are very few commercial software programs which fall into this class, but there are many public domain and shareware programs that are generic DOS, and which will run on the Z-100.

Can the Z-100 Run IBM-PC Software?

There are several approaches to using IBM-PC software on the Z-100. First of all, many "PC programs" are really not IBM-PC specific, but are programs which will run on any MS-DOS computer, including the Z-100 (see previous question). In order to fall into this category, a program has to display only text (no graphics), use only ASCII keyboard input (text character keys or control codes), and access peripheral devices using MS-DOS function calls. It will be almost impossible to tell if a program is a generic DOS program without trying it.

For PC-specific programs, there is still hope for running them on the Z-100. The most economical approach, and the logical first alternative, is to try a ZPC software emulator program developed by Patrick Swayne, an engineer at the national Heath User's Group or HUG.

This program has continued to be developed and updated over the years since and allows you to use a surprising number of IBM-PC programs on the Z-100. Many programs will run under ZPC without any problem. Others may require modifications, called patches, before they will perform correctly. For this reason, the ZPC software solution may not be a good choice for casual users unless the application programs you need will run without patching. The ZPC program requires at least 768K of RAM memory (the full load) for the most successful emulation. The latest versions of ZPC are still available from the "Z-100 LifeLine". Contact information is provided at the end of this article and on this website.

If you wish to obtain the ZPC emulator program, you might also consider upgrading to Z-DOS v4 and the new MTR-100 monitor ROM chip, or a "Scottie Board".

While the computer processing unit or CPU might be considered the heart of any computer, the monitor ROM is the brains. It controls the operation of the computer after power-up, initializes the necessary I/O ports and determines which CPU will be active in the monitor mode. It also contains the character sets and other important data to be used by the CPU.

The latest version of the MTR-100 monitor ROM is available from the "Z-100LifeLine" and contains some PC compatibility features which may be helpful in running PC software on your Z-100.

The "Scottie Board" was a daughter board that plugged into the motherboard in the Z-100's card cage. It provided some hardware support for the ZPC emulator to improve PC compatibility.

Neither of these products is required to use ZPC, but they improve the odds of providing the compatibility that you seek. The "Scottie Board" is no longer commercially available.

At least two companies have developed elaborate hardware solutions for the Z-100 PC compatibility problem. Gemini Technologies had a product called the Gemini Emulator Board, and UCI Corporation manufactured the UCI Easy-PC Emulator. These hardware modifications to the Z-100 allowed just about any PC compatible program to be run on the Z-100, as long as it uses text or CGA graphics modes. Neither of these products remain commercially available, so contact the "Z-100 LifeLine" for availability.


Operating Systems for the Z-100

What Versions of DOS Does the Z-100 Use?

It goes without saying that you MUST have some operating system to use the Z-100.

When the Z-100 was first introduced back in 1982, Zenith provided their own version of MS-DOS v1 to use with it. They called it "Z-DOS". This has caused some confusion, since in subsequent versions, Zenith dropped the Z-DOS designation, and simply referred to it as Zenith's version of MS-DOS. So many people who have Z-DOS don't realize that they really have MS-DOS v1.

If Z-DOS is all you have, at least you're better off than others who have nothing at all. But you should strive to find a later version of MS-DOS for your machine. Beginning with version 2 of MS-DOS, important features were added which prevented most DOS programs from running under the older version1.

The latest version of DOS available for the Z-100 is Z-DOS v4.06, developed mostly by John Beyers of the "Z-100 LifeLine" staff.

Perhaps the greatest improvement of Z-100 compatibitity and usefulness came from this upgrade to Z-DOS v4. This version bears little resemblence to earlier DOS versions and uses much of the capability of MS-DOS version 6 for the PC-clones. It also includes support for high density 3.5" floppy drives and the new IDE drives when coupled with the new IDE controller, which includes a bootable NVsRAM and clock capability.

Earlier versions still available from the "Z-100 LifeLine" are DOS v2 and v3. But keep in mind that these must be versions which are designed to work on the Z-100. You can not take your brother-in-law's copy of MS-DOS 3.1 and expect it to work on the Z-100.

Also note that the PC-emulator systems, Gemini and Easy-PC, mentioned above require a Zenith version of PC-DOS to be used. These are also still available from the "Z-100 LifeLine". To make some sense out of all these versions of DOS, I now have a policy of calling all versions of DOS for the native Z-100, "Z-DOS" with the version number, for example "Z-DOS v2.1". I call all the Zenith PC versions of DOS for the Z-100 in PC mode, "PC-DOS" with the version number, for example "PC-DOS v3.1" I call all the non-Z-100 DOS versions meant for PC-clones simply "MS-DOS". I hope this avoids the confusion in the future. 

Are Other Operating Systems Available?

Yes. In fact, the Z-100 probably has a wider range of operating systems to choose from than any other microcomputer system. Due to the presence of two processors in the Z-100 (an Intel 8088, plus an Intel 8085) the Z-100 can accommodate 8 bit, as well as 16 bit operating systems. Examples are:

MS-DOS               CP/M-85                  CP/M-86                      Concurrent CP/M-86

H-DOS                  CP/M Plus               UCSD Pascal               and possibly others

I don't have enough space here (or the knowledge, really) to go into detail about these other operating systems which have been available. Check with the "Z-100 LifeLine" for availability.


About the Hardware

What Do the Rear Panel Connectors Do?

Here is a listing of each connector on the back panel, and a description of its use:

  • J1    -  This is a female DB-25 connector which serves as a DCE (Data Communications Equipment) port. It was originally intended to be used as a serial printer port, although many serial printers are more conveniently connected to J2.
  • J2    - This is a male DB-25 DTE (Data Terminal Equipment) serial port. It may be used for serial modems, printers, or other devices. This port is roughly equivalent to the COM1 port on PC compatibles. Both serial ports in the Z-100 (J1 and J2) are similar, and differ primarily in the gender of the connector and the pin-outs. Most devices can be used on either port if you have a null-modem gender changer.
  • J3    -  A parallel printer port which uses a female DB-25 connector. This is a standard parallel output port similar to the LPT1 port on PC compatibles. However, please note that it is NOT bi-directional.
  • J4    -  A modular phone jack which is used as a light pen connector. Use of a light pen with the Z-100 will require special software which knows how to interface directly with the light pen. It is NOT a modem port.
  • J9    -  This is a female DB-9 connector used for RGB video output to a color monitor. Most CGA compatible color RGB monitors should work okay with the Z-100, and should come with this type connector. However, those monitors meant for PC-clones use positive sync signals, instead of the Z-100's negative sync. Fortunately, the Z-100's video board can be set by jumpers to provide the necessary positive sync signals. (More later when we discuss monitors)
  • J14  -  An RCA phono jack used for monochrome video output to a monochrome monitor. This jack is replaced by a brightness control on All-In-One models, since the composite monochrome monitor is built in.
  • J16  -  If installed, this should be a 50-pin connector for attaching a Shugart compatible 8 inch floppy disk drive. However, if the Z-100 has previously been attached to a Bernoulli Box, tape backup, or other special equipment, J16 may be used as a 50-pin SCSI bus connector.
  • There are knockouts for many more connectors on the back panel of the Z-100, but stock machines will only have those listed above. The existence of additional DB-25 or other types of connectors probably means that a multi-port I/O card (Z-204) or other accessory cards are installed.
  • If one of the rear panel knockouts has been replaced by a small slide switch, the switch is most likely used to change the Z-100 between 4 Mhz and 7.5 or 8.0Mhz operation.


What Does DIP Switch S-101 Do?

DIP Switch S-101 on the Z-100 motherboard is used to select the default boot device, whether auto-boot is used, and whether the power supply is 50 or 60Hz. Here is how the switch sections are defined:

  • Sections 0 through 2 are used to determine the default boot device. Setting these first three switch sections to 0,0,0, will cause the Z-100 to boot from the 5-1/4 inch floppy drive. Using 0,0,1, specifies boot up from the 8 inch drive. And 0,1,0, will cause the hard drive to be used as the default boot device.
  • Beginning with monitor ROM, MTR-100 v3.1, setting these switches to 0,1,1, permitted the Z-100 to boot from an EPROM device on the LifeLine's SCSI controller board. With MTR-100 v4.3, support was added to boot from the IDE controller's NVsRAM.

Note that regardless of the setting of S-101, you can still boot from any device by explicitly giving the commands from the hand prompt. These will be discussed in detail later.

  • Section 3 of S-101 is used to specify that the computer should auto-boot. Setting section 3 to 1 will cause the Z-100 to attempt to boot the default boot device when the power is turned on, or whenever a {CTRL}-{RESET} is initiated. Setting the switch section 3 to zero, the manual boot position, will result in the hand prompt appearing whenever you power up or {CTRL}-{RESET}.
  • Sections 4, 5, and 6, of S-101 are not used in a stock Z-100. They are, however, readable by software (as port OFFh). So there may be third party software which uses these switch sections for some purpose.
  • S-101 section 7 should be set to 1 if your A.C. power supply is 50 Hz. Leave this switch off if you have standard 60 Hz power (i.e. in the United States).

What Kind of Printer Will Work?

The Z-100 has two RS-232 serial ports, and one parallel port. Since these three I/O ports are right on the Z-100 motherboard, you can rest assured that every Z-100 has them. Therefore, connecting and using a printer is fairly easy.

Any printer with a standard Centronics type parallel interface should work just fine when connected to a Z-100. It should be connected to J3. If you have a printer with a serial interface, plug the cable into whichever connector (J1or J2) is the right gender. Essentially any printer which is advertised as compatible with the IBM-PC should work on the Z-100.

Keep in mind that the version of DOS provided by Zenith for the Z-100 may need to be configured before your printer will work. See the section titled "Configuration" later in this Guide for more information.

What Kind of Video Monitor Can I Use?

The first consideration when choosing a monitor for your Z-100 is whether you want a monochrome or color system. The Z-100 has the capability to drive either a monochrome composite video monitor, or a digital RGB color monitor. An RCA type phone jack is provided on the back panel for connection of the composite video monitor. And a DB-9 connector is provided for RGB monitors.

Note:  The All-In-One Z-100 has a monochrome monitor (yellow or green) built into the case, and has a brightness control in place of the RCA plug, but it also includes the connector to add a RGB monitor.

Any composite video monitor should work well with the Z-100. The composite video output of the Z-100 is the same type of signal as the outputs on a VCR, except it is monochrome. In fact, you can even use this video output from the Z-100 to record screen displays on your VCR tapes.

Any digital RGB monitor advertised as being compatible with the IBM-PC CGA graphics adaptor should work on the Z-100, except that the sync signals may be different. While the Z-100 uses negative vertical and horizontal sync signals, the IBM-PC compatibles used positive signals. These can be adjusted via jumpers on the Z-100's video board.

Also, since the Z-100 has considerably higher graphics resolution than CGA, you will probably want to buy a video monitor at the high end of the quality scale. A cheap monitor will typically not have a small enough dot pitch to render a sharp display on the Z-100.

If you are looking for a color monitor, there is probably some justification for purchasing one of the auto-synchronizing type of video monitors (like the NEC "Multisync"). These make excellent monitors for the Z-100, and have the added advantage of being portable to a PC compatible system (with EGA or VGAcard) if the time ever comes.

Can I Add a Hard Disk to the Z-100?

Sure, no problem. But your choices are currently limited. Most drives of the time were MFM and are becoming increasingly difficult to obtain. In the past, there have been many different hard disk interfaces available for the Z-100. Examples are the Zenith Z-217 Winchester Controller with a separate Data Separator Card, the CDR-317, and the UCI Easy-WIN.

All of these devices would allow you to boot from the hard disk unit. Many other S-100 based hard disk controllers would potentially work with the Z-100, but would provide no boot-up support.

If you can find one of these existing hard disk interfaces on the used market, you may be in good shape. Any of the interfaces mentioned above will work with a standard MFM hard drive (for example, the Seagate ST-225). Be prepared, however, to pay a premium price for a used hard disk interface... since theyare in short supply. As an alternative, you might want to shop for an entire used Z-100 computer that already has a hard disk installed.

Other alternatives to the hard disk dilemma:

The SCSI Host Adaptor and Bootable EEPROM board was a project sanctioned by "Z-100 LifeLine" to use SCSI drives. The LifeLine SCSI board provided a bootable hard disk interface with complete documentation and offered an open-ended path to future SCSI devices. These controllers are no longer in production, however, and are in very tight supply.

A new, IDE controller has been successfully developed by "Z-100 LifeLine" staff and a few boards are still available. The Z-100 IDE Controller Board uses all older IDE drives except the latest UltraDMA models. If you have any desire to obtain one of these, contact the "Z-100 LifeLine" immediately. Once these are gone, there will probably be no more.

Can I Read/Write PC Compatible Disks?

Yes, both the Z-100 and IBM-PCs used the standard 360K, double sided, double density format. These disks are interchangeable between machines. If you find that you cannot read disks created in a PC compatible machine, there are several things to check:

  • Make sure the PC compatible disk is a standard 360K format disk. Many PC computers (especially the ATs) used a high density 1.2 Mb format which cannot be read by the Z-100.
  • Check your version of DOS. If you are using MS-DOS v1 (also known as Z-DOS v1 on the Z-100), you will not be able to read disks created with version 2 or above of MS-DOS. This is because version 2 and higher of MS-DOS used 9 sectors per track, instead of the 8 sector format used by Z-DOS.
  • In some cases, inability to read a known-good diskette may be caused by hardware problems, such as a drive which is not aligned properly, or a bad controller board. If the Z-100 seems to work just fine with its own disks, but refuses to read disks created on other machines, you may have an alignment problem.

If PC disk compatibility is a primary concern, and you need to read high density or 3.5 inch formats reliably, early software, such as DiskPack, provided some interchange capability, but suffered reliability issues. The best option available is to upgrade to Z-DOS v4 with new MTR-100 Monitor ROM v4.3 (discussed earlier) and a modified Z-207 floppy controller. The cost is reasonable and all floppy formats are available. Z-DOS v4 DSKCOPY4 provides unique copy and disk image making capability.

Getting Started Without Documentation

Many Z-l00s are being sold without any documentation or user's manual. It is easy to understand why the new purchaser would have difficulty figuring everything out. The remainder of this section is a step-by-step guide for getting a Z-100 up and running, with or without documentation.

Power-Up Check

The only thing you'll need for this check is the Z-100 itself, and a video monitor. If you have the "All-In-One" model, your monitor is built into the computer. If you have the "Low-Profile" model, you'll need either a composite monochrome monitor, or a CGA compatible RGB color monitor. Plug composite video monitors into the J14 RCA plug. Plug RGB monitors into connector J9. Sorry, the Z-100 won't work with a TV set (former Commodore 64 owners ask this question from time to time).

The power connector on the back of the Z-100 is a standard type used by many computers. If you need a cable, try a local electronics parts house.

Now plug the Z-100 in, and turn it on. You should hear one or two BEEPs(depending on ROM version). You should also hear a noisy fan coming up to speed. No Fan noise or BEEPs? This probably means the power supply is dead. Yes, the Z-100 has a fuse, but it is within the power supply itself and is considered to be a non-serviceable part (no, this is not a joke, it is Heath/Zenith's way of selling power supplies).

At any rate, if the fuse is blown, you've probably got other problems. Contact the "Z-100 LifeLine" for assistance.

If you hear the fan, but no BEEPs, then there is something wrong with the internal electronics. It could still be the power supply, but before you give up completely, take the cover off (see below for instructions) and try wiggling all the sockets and connectors to see if that corrects the problem. Still no luck? Unless you're an electronic technician, you're up the proverbial creek without a paddle. Complete service documentation and schematics, however, are available from the "Z-100 LifeLine".

If the Z-100 does BEEP at you, all is well so far... skip the next section.


How To Take Off The Cover

If you need to get inside the Z-100, the cover is easy to remove, but only if you know how.

Look at the back of the computer, and on each side you should see metal rails sticking out. Grab these and pull them toward the back of the machine and lift the lid at the same time. You may need to use a screw driver or a pair of pliers to get them moving if they're stuck. The lid should just lift off. Note:  Only move the slides back about 1/4". If you pull them too far back, this is the "locked" position.

After the cover is off, you'll have access to quite a bit of the internal electronics of the machine. You still won't be able to get at some of the boards without further disassembly, which is beyond the scope of this paper. If you have the guts and the desire, go for it! Z-100s are easy to take apart and put back together - just make sure you remember which connectors go where and which side of the ribbon cables are marked. Take copious notes as you disassemble. More complete disassembly instructions are available on this website.


The Hand Prompt

Note:  Some Z-100s (particularly those with a hard disk installed) may be set for automatic booting. If this is the case, but you would still like to follow along with our discussion, try pressing the {DELETE} key during the auto-boot sequence, and you should be returned to the hand prompt.

Note:  The braces "{}" here and in the discussion to follow are used only to differentiate a key name from typing individual letters, such as {SPACE} or the {F4} function key. Do not type them as part of a command.

After the BEEP(s), you should be able to see a prompt on the video monitor that resembles a hand with a pointing finger. If you don't, check your video connections again, and make sure you are using the proper type of monitor. If you still don't get anything, it sounds like problems with the video board in the computer. This could be something simple like a connector which fell off in the machine, or it might be more serious. If you want to have a look inside, proceed at your own risk.

If you get a video display, but it is distorted or out of sync, check the adjustments on your monitor first. If the problem can't be corrected by adjusting the monitor, you may have to fiddle with the jumpers on the videoboard. The video board is mounted horizontally and inverted over the motherboard. Jumpers are provided to select the vertical and horizontal synchronization polarity, and the type of RGB synchronization.


System Information

Now it's time to find out something about the configuration of your Z-100. When the hand prompt is displayed on the screen, press the {S} key. Depending upon the version of monitor ROM installed, the computer should display a few lines of information about how much memory is installed, what type of video memory is used, and if the system is color or monochrome. It may also tell you what size memory chips are used, and if you have an 8087 numeric coprocessor installed.

Now, press the {V} key. This will tell you what version of the monitor ROM you have. If you have a Winchester hard drive installed, or plan to add one later, you MUST have version 2.5 or later of the monitor ROM.

Press the {HELP} key. You should see a list of all the valid ROM commands. You can play with some of these if you like - it won't hurt anything. The exact details of how to use most of them are again beyond the scope of this article and will be left as an exercise for the user. However, one which may be particularly useful is the TEST command. If this option does not appear on your list of commands, then you must have a real old version of the ROM - don't worry about it for now. If this option is available, try it. You should get a second menu showing the different tests which are available. Options should include a disk read test, keyboard test, memory test, and power up test. There's no need to run these tests right now, but make a mental note that they are available, if needed.


Booting Up

If you've gotten this far, you can take confidence that most of the computer is functioning as it should. The only major parts that could still cause problems are the disk drives and controllers.

If there is a hard disk (often called Winchester in Heath/Zenith documentation) installed in the Z-100, try just typing {B} (the computer will complete the command by adding 'oot', and press {RETURN} to see if the hard drive is set up as the default boot device. If the DOS sign-on message appears, you are home free - the previous owner must have left the system software on the hard disk.

If your system does not have a hard drive, or if the Winchester hard drive boot attempt failed, we will have to boot from a floppy disk. Find your MS-DOS (or Z-DOS... Ughhh!) distribution disk, and insert disk #1 in floppy drive A. Drive A is usually the one on the left (systems with full-height drives), or the one on top (All-In-One Z-100s, or systems with half-height drives).

If you have a Z-100 with a hard drive, you only have one to pick from, and it must be drive A.

Now try typing {B}, followed by {RETURN}. Or, if you have a hard drive system, you may have to type {B}, then press the {F1} key, and press {RETURN}. The drive A access light should come on, and the system should boot up and display the DOS banner.

Note:  The function keys {F1}, {F2}, {F3} and {F4} select a particular boot device, if installed. For example, the {F1} key tells the computer to boot from a 5-1/4" floppy drive. The {F2} key would tell the computer to boot from an 8" floppy drive. The {F3} key would boot from the hard drive and the {F4} key would boot from the EEPROM or NVsRAM board, if installed.

If the computer waits for a long time and then displays "DEVICE ERROR", you may have hardware problems with the drive or controller board. If the computer just hangs forever, crashes back to the hand prompt, or does other crazy things, you're probably trying to boot with an improper version of DOS. Remember, you must be using Z-DOS or a MS-DOS specifically for the Z-100!

If you get the message "NO SYSTEM", this means the disk you are trying to boot is not bootable. If you have an unlabeled two-disk set of DOS disks, try the other disk.



If you have successfully booted DOS, you are just about home free. One other thing that will be necessary before you can use any printers or other peripheral devices is the DOS configuration. This is not normally necessary with PC compatible computers (or is done with the MODE command), but on the Z-100, you MUST configure DOS for the devices you will use.

Find the CONFIGUR program on one of your DOS disks. Run this program and follow the instructions. Typically, you would want to configure DOS to use a parallel printer as device PRN, and maybe a serial printer or modem as device AUX. Before exiting the CONFIGUR program, be sure to write the changes to DISKand MEMORY. This is an option on the main CONFIGUR menu. This configuration process must be done for each bootable DOS system disk you use, including each bootable hard disk partition.

To check out the configuration, try just copying some text to the printer using DOS. This can be done as follows:

1.  At the DOS prompt, type: COPY CON PRN{RETURN}

2.  When the cursor goes to the next line, type in some characters, like "Testing 1,2,3" and press {RETURN}.

3.  Enter a Control-Z character. This is done by holding down the {CTRL} key and pressing {Z} at the same time. Then press {RETURN}.

4.  The text you entered should be printed on the PRN device (the printer).

You can also configure and test the AUX device in the same manner.


Accessing Already Bootable Hard Drive

At this point, you are basically in business. You should now be able to use any of the programs that you have for the Z-100. But if you have a hard drive system, and you were NOT able to boot onto the hard drive, there is still work to be done.

Try typing {B}, followed by {F3}, a colon {:}, then your name, and {RETURN}. This tells the computer that you want to boot-up (B) from the hard drive (F3) onto the partition with your name. Needless to say, it will not find a partition with your name (unless your name is something like Ms. DOS).

You should receive a message that says:

"Error - Partition Not Found.

Hit RETURN to continue"

Follow instructions, and press {RETURN}. You should now see a list of the valid hard drive partition names.

Try booting to each of the partitions that are listed by using the {B}ooting procedure above, but use the partition name, instead of your name. Hopefully, you will find one that is bootable.

If you don't get a list of partition names, this generally means that the hard drive needs to be prepared from scratch. This involves running the PREP program, and the PART program. These utilities are included with the Heath/Zenith Winchester utilities, on a separate disk usually provided with the hard drive. These programs are available from "Z-100 LifeLine".

PREP is a program for the Z-100 which does a low-level format of the hard drive. In order to use PREP, you will need to know all of the intimate details about your hard disk, such as number of heads, number of cylinders, reduced write current cylinder, write precompensation cylinder, parking cylinder, and step rate. This information should be included with the hard drive, but if you don't know it, contact "Z-100 LifeLine" with the drive's model number.

PART is Zenith's program which is used to divide the hard drive into logical partitions which can be treated just like separate drives. Each partition must have a partition name, an operating system name, and must specify the percent of the hard drive it occupies. It is probably a good idea to use "Z-DOS" for the operating system name, since this will allow Z-DOS to recognize the partition. Later versions of DOS don't care about the operating system name listed in the partition table.

Accessing Winchester Hard Drive Partitions

If you have been unsuccessful at booting onto the hard drive, you will need to access it by booting from a floppy drive. Make sure you have gone through the procedure described above, and written down the names of any partitions found.

To access the hard drive partitions, you will need a Heath/Zenith utility program that assigns drive letters to the partitions. The name of the assignment program is ASSIGN if you are using MS-DOS v2 and ASGNPART if you are using DOS v3 or greater. If you are using Z-DOS (MS-DOS v1), all partitions with "Z-DOS" listed as the operating system should be assigned automatically by DOS (up to a maximum of 4 partitions). In this case, you can skip the rest of this discussion about "assigning" partitions.

Boot up on your system floppy, and run the assignment program using the following syntax:



0          = the hard drive unit number

Pname = name of partition to assign

d:         = drive letter to assign

The drive letter you assign should be E, F, G, or H.

Note:  If you neglected to write down the partition names, just using the command:


will list the partition names for you.

After executing this command, you should be able to get a directory of the hard drive partition in the same manner as any other disk. If not, this generally means that the partition has not been formatted, so you will need to use the DOS FORMAT program to format the partition. Remember to use the FORMAT '/s' switch for any partitions you want to be bootable.


Wrapping It Up

I hope this information will help you get your 'new' used Z-100 on line. The "Z-100 LifeLine" has a Z-100 software library with hundreds of programs and applications to make your purchase very productive. It also has an Archive Software Library that can be used to replace any damaged copyrighted program 5-1/4" disks or create new boot disks.

After getting your Z-100 working, one of the next things you should do is start a search for any documentation you can find about the Z-100. This would include the Z-100 Users Manual, Z-100 Technical Manual Set, MS-DOS Reference Manual, Programmer's Utility Pack, and back-issues of "REMark" and "SEXTANT" magazines, as well as "Z-100 LifeLine" newsletters.

There are lots of other options, jumpers, and DIP switches in the Z-100 which have not been mentioned in this article. Many of these will have an affect on the way the system operates, and how useful it is for you.

I know that this all seems like a lengthy commercial for "Z-100 LifeLine", but I can not mention enough that most any support that you will need can be found here. All you have to do is ask.

If you have any questions, contact me at:

Steven W. Vagts, Editor, "Z-100 LifeLine"

211 Sean Way, Hendersonville, NC  28792

(828) 685-8924

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Website: https://z100lifeline.swvagts.com


The web site has answers and background information that you may be seeking and provides links to some important sites. I also have parts, software, and documentation available at reasonable prices.

"Long live the Z-100!"


H/Z-100 Keyboard Key Repair

General Notes:

  • This article was published in the May-June 1994 issue of the "Z-100 LifeLine", issue #33.
  • WARNING:  The following fix requires some knowledge of electronics and soldering skills! Try this ONLY AT YOUR OWN RISK!
  • WARNING:  All-In-One users MUST KEEP CLEAR of the CRT power cables, the CRT second anode (the thick single cable going to the top of the CRT) and the high voltage transformer on the vertical video board during computer operation. Voltages in these locations are DANGEROUS.



One of the most common and frustrating problems encountered with the Z-100 series computer is with the keyboard. It seems that all of them eventually have a key that no longer functions, or gives multiple characters when pressed. Cleaning is also a challenge and can cause problems if not done very carefully.

Fortunately, there is an inexpensive fix for malfunctioning keys that has a 90% or more success rate. The fix is easy, but does require soldering skills. Also, set aside a few hours of uninterrupted work as this involves disassembly and reassembly of the computer. A fancy desoldering gun is not required, as a squeeze bulb or desoldering braid works nearly as well.

Tools  (in addition to those needed to disassemble the computer):

  • Vacuum cleaner
  • Small, 1" or less, paint brush
  • Ohmmeter
  • Soldering gun (or iron) and solder
  • Desoldering gun, squeeze bulb, or desoldering braid
  • Two metal paper clips
  • Dental pick, if available
  • Small jeweler's screwdriver
  • Small needlenose pliers

Disassemble the computer in accordance with Chapter 1 of the Z-100 Users' Manual until the keyboard can be removed from the computer. Disconnect the two ribbon cables attaching the keyboard to the motherboard at the motherboard. They just pull straight up, but may require some gentle prying at each end. Remove the keyboard.

Though the keyboard need not be removed for cleaning, now is a good time to do that.

CAUTION:  DO NOT spray the interior of the keys with any kind of cleaner or lubricant such as WD-40. The cleaner or lubricant will leave a film that will damage the key's delicate interior.

Using the paint brush to loosen stubborn dust and the vacuum cleaner, vacuum the top of the keyboard, concentrating on the area under the key caps. Using a terry cloth or hand towel, soak a small section with a strong cleaner. I find 409 is excellent. Carefully, rub the top and around each key individually.

Noting the location of the malfunctioning key or keys, select the solder lugs that belong to those keys. Place the keyboard, inverted, on a towel on the work table. Remove the solder completely from these lugs using a desoldering gun, desoldering squeeze bulb, or desoldering braid, until the lugs move freely in their holes. Figure 1 shows the mounting of a couple of keys in the keyboard. Figure 1(a) shows the view of a fully installed key.



Flip the keyboard over. Straighten the two paper clips and form a 1/4" hook on one end of each using the needlenose pliers. Insert them under opposite sides of the malfunctioning key cap and remove the key cap by pulling straight up, gently - figure 1(b).

Study the revealed key switch. Figure 1(c) gives top and side views. On each side of the switch, and as shown by the arrows, is a broad plastic catch lever that retracts toward the center post to release the switch from the keyboard bracket. With the small jeweler's screwdriver, press one of these levers toward the center post. Release it and it snaps back into place. The object is to retract these levers while pulling the switch gently from its socket - no easy stunt. Pressing the solder lugs up from the bottom while pinching the levers together toward the switch's center post will usually work. An alternative method against a stubborn switch is to pry up on one wing of the switch by wedging a dental pick under it from the top, while pressing the lever of the switch on the same side to the center. Then do the same from the other side. Unless the key is on an edge, all work will have to be done from the top.

Once removed, the tough part is over. The switch is encased by a plastic cover on all sides except the top, which is separate. See figure 2. Clean off any remaining solder from the solder lugs as this case must be removed over these lugs.



Two sides of the switch case mate and interlock with the top cover. They can be carefully pryed away from the edge of the top cover, first one side, then the other, and the case then slid down the solder pins and removed. The remaining insides are simple - a spring, a centerpost slide and the wafer switch itself with the solder lugs attached.

Examining the insides, the centerpost slides down when pressed, placing pressure against the metal inverted "Y" leaf spring that then presses against the body of the wafer switch. In more than 90% of the cases, I have found that this inverted "Y" doesn't make firm enough pressure against the switch body to close the switch. To increase this pressure (unrelated to spring pressure) the bent angle of the inverted "Y" simply needs to be increased slightly.

Using a small pair of needlenose pliers, grasp the inverted "Y" at the free-end side of the existing bend and increase the bend slightly. Bending too far will make the key feel stiff when pressed and, if exaggerated further, may even interfere with the spring, jamming the key.

It is easiest to assemble the key case from the top down, imagining an inverted Figure 2.  Insert the white centerpost into the inverted top cover. Next insert the wafer switch itself, with the lugs sticking out and the inverted "Y" towards the centerpost. Pressing up on the centerpost should compress this inverted "Y" into the wafer switch. On the opposite side of the centerpost, insert the spring into the round recess. Finally, gently lower the key case over the solder lugs until the sides interlock with the edges of the top cover.

Before reinstalling the key into the keyboard, check the switch with an ohmmeter. Connect the leads of the ohmmeter across the solder lugs; the resistance should be infinity. Press the switch and the resistance should instantly drop to zero ohms. If it doesn't, recheck the assembly of the switch. The centerpost must compress the Y against the wafer switch.

If the switch is still inoperative, another can be ordered from me, or other remaining Z-100 hobbyists.

The switch is reinstalled in the keyboard by aligning the solder lugs with the solder holes on the circuit board and pressing down until it clicks into place. The lugs are offset so the switch can only be installed in one direction. The key cap is simply pressed on. Solder the solder lugs to the backboard and you're in business.

Before reassembling the computer, press the keyboard cables onto their motherboard connectors, connect an external monitor to the backboard or, in the case of the Z-120 All-In-One, gently place the monitor assembly onto the computer's base frame (Be very careful, but the monitor assembly will fit nicely on top of the metal sides), without the bottom cover installed, and connect the power cable to the vertical video driver board on the left side. Don't worry about the drives' data or power cables. You just want to try the keyboard. During the following test, All-In-One users MUST KEEP CLEAR of the CRT power cables, the CRT second anode (the thick single cable going to the top of the CRT) and the high voltage transformer on the vertical video board. Voltages in these locations are DANGEROUS.

Turn on the computer and at the hand prompt, press {T} for Test. Perform the keyboard test to ensure all keys operate normally. If not, fix these keys as above and retest.

Finally, reassemble the computer per the Users' Manual.


There are a few special keys, but the basic construction is the same.

The {CAPS LOCK} key is much more complex than a normal key. It is constructed with an additional leaf spring and a wire clip that, in combination with the special centerpost, keeps the key depressed until another tap releases it. The spring just beneath the key cap provides the key tension. The top of the spring fits in a hole about 1/2 way up the centerpost. See Figure 3.


ZKey3          ZKey4

The {RESET} key is also more complicated because it has a light emitting diode (LED) installed. See Figure 4. If this key fails, removal is the same as above, except there are four solder lugs - including two for the LED. The metal bracket fits over the top cover.  If the ohmmeter test confirms failure, it is probably best to just order a replacement.

Steven W. Vagts, Editor, "Z-100 LifeLine"


SmartWatch Dead Battery

General Notes:

  • The following article appeared in issue #120, March 2012, of the "Z-100 LifeLine".
  • Some real electronics experience and soldering skills are necessary.
  • Click on the drawings to magnify the image.

The Case of the Dead SmartWatch

By now, you have probably noticed that your SmartWatch no longer keeps time! Actually, this should be no surprise, because the lithium battery was only predicted to have a life of about 10 years. As we are nearly 30 years since the introduction of the Z-100, I was surprised the clocks lasted this long.

So what can we do with the remaining carcass?

It would be a real shame to dump the SmartWatch because of a bad battery, so I did some research and played around with one of mine.

First, the bad news. These lithium cells are dangerous, hence the following warnings:

WARNING:  Do NOT go poking around a lithium cell or try to dismantle the SmartWatch. These battery cells have been known to short out and explode. I measured the voltage remaining in one of my SmartWatches and found that the voltage was still about .7 to .8 volts.

WARNING:  Do NOT attempt to recharge these lithium cells either. Recharging could cause the cells to explode.

So, what to do? First, let's review some SmartWatch specifications:


The DS1216E SmartWatch is an assembly containing non-volatile (NV) RAM with a built-in CMOS watch function and two lithium cells contained in a 28-pin DIP socket that mounts under the monitor ROM in the Z-100.

The SmartWatch ROM sockets use the embedded lithium source to maintain the time and date only. The SmartWatch monitors the computer's +5 Vdc power at pin 28 of the ROM chip and when the voltage drops to below the battery's voltage, the internal lithium energy source is automatically switched on and write protection is unconditionally enabled to prevent loss of watch and NV-RAM data.

The SmartWatch is based on the Maxim DS1315 clock controller chip with two energy cells, one attached to pin 4 and the other attached to pin 14 of the DS1315 chip. As the energy cells are ONLY attached to the clock chip,the predicted energy drain was such that the cells would last about 10 years.

Each DS1216 was shipped from Maxim with its lithium energy source disconnected, ensuring full energy capacity when finally used in the computer. When computer power is first applied at a level greater than the lithium energy source, this energy source is enabled for battery-backup operation. During my research, I found no means to turn the cells off.

NOTE:  The DS1216E has been discontinued and is no longer available from Maxim, but according to the Internet, some of these still appear to be out there for sale. So, a word of caution. As you have no way of knowing whether a SmartWatch has been activated (used), the SmartWatch that you receive may already be on its last legs, if not already dead.

Finally, the lithium cells are isolated from computer power, so there is supposedly no danger of charging the cells under normal use.

Further information on operation of the clock can be found on the Internet from Maxim.

Ok, enough preliminaries.


The ideal means of powering the SmartWatch would be to disconnect the energy cells from the DS1315 clock controller by cutting pins 4 and 14, then attach our own external battery to the pin stubs. However, upon looking more closely at the SmartWatch socket, there is no chance of disconnecting the energy cells from the DS1315 chip without causing extreme damage to the socket, which surrounds the DS1315 chip quite tightly.

So, our only recourse is to simulate computer power to the SmartWatch. However, the downside of this method is that we are not only powering the SmartWatch, but also the ZROM pins and other computer circuitry. This drains any battery much faster than if we were just powering the clock oscillator. Instead of lasting years, the new battery backup may only last hours.

On the positive side, I don't use my Z-100's all that much, and when I do, I'll work on any one of several for several days, with multiple power-ups each day as I test various components and configurations. Then I move on to something else and it may be weeks or months before I work on that computer again. Any battery would be long dead before I used the computer again. I just hate resetting theclock several times over the course of my work.

Rethinking the issue, I reasoned that if I could get the clock to last for about an hour, long enough to change a part or configuration, I'd be happy. This would be an ideal use of a supercapacitor! I had seen this as an option for the Scottie Board clock.

The new circuit is simple. We want to minimize the power drain, so we need to disconnect the SmartWatch socket's pin 28 from the computer's +5 Vdc Vcc and feed that pin separately - from our supercapacitor.

Likewise, to reduce the power drain of the Monitor ROM, or ZROM, we need to disconnect pin 28 of the ZROM and feed it separately from any other +5 Vdc source - another nearby integrated circuit.

We need to insert a diode in the capacitor's charging circuit to prevent powering the computer's entire +5 Vdc bus from the freshly charged capacitor when the computer is shutdown. The internal resistance of the diode also controls the charging current.

Required Parts:

1    - 1 Farad, 5.5v Supercapacitor

1    - Diode, such as the 1N4003

4"   - Black hook-up wire

20"  - Red hook-up wire

1/2" - 1/8" shrink tubing

1"   - 1/4" shrink tubing

1"   - doublestick or electrical tape

Tools Needed:  (In addition to those needed to dismantle the computer)

IC remover or thin flat-bladed screwdriver

Solder gun or iron w/solder

Philips screwdriver



[  ]  Disassemble the computer down to the motherboard.

[  ]  Remove the three screws holding the video board and fold the board back up against the card cage.

[  ]  Referring to Figure 1, remove the ZROM from the SmartWatch at U190,

[  ]  Remove the SmartWatch from the U190 socket

[  ]  Bend pin 28 out on the SmartWatch socket and reinstall it into the U190 socket

[  ]  Likewise, bend pin 28 out on the ZROM, then reinstall it into the SmartWatch socket.


Figure 1.  SmartWatch Removal

Construct the following circuit using a 1 Farad supercapacitor, available from Mouser and Digi-Key for less than $5.00 and pretty much any diode. I used a 1N4003 from my junk box, but nearly any diode will do. Just check that the diode's reverse resistance is as high as possible to reduce current drain.


[  ]  Using doublestick tape or doubled over electrical tape, mount the supercap to the left side of the computer's metal bottom case in front of the power supply.

[  ]  Mount the diode directly to the positive lead of the supercap. Double check that you have the polarity of the diode and capacitor correct. If the diode is reversed, the capacitor will not charge and the SmartWatch cannot receive power.

CAUTION:  Don't touch the leads of a charged supercapacitor. While we are only playing with 5 volts dc, the current can be high enough to spark and give you quite the jolt!

[  ]  Slide about 1/2" of 1/8" shrink tubing over a 4" length of black wire and solder a spade lug to one end. Attach this end to one of the two base mounting screws of the power supply.

[  ]  Solder the other end to the negative lead of the supercap. Slide the shrink tubing over this lead.

Since I didn't wish to cause problems by drawing charging power from one of the integrated circuits of the motherboard, I used one of the 5 volt lines at the power supply connector for the motherboard. It is easy to get to with the soldering iron without removing the motherboard.

[  ]  Solder one end of a 7" length of red hookup wire to one of these 5 volt terminals.

[  ]  Slide a 1" length of 1/4" shrink tubing over the other end of this wire and solder this end of the wire to the diode. Don't slide the shrink tubing over this yet.

[  ]  Slide one end of a 10" length of red hookup wire through the shrink tubing and solder this end to the positive lead of the supercapacitor. Check to ensure the diode is still soldered in place here also.

[  ]  Slide the shrink tubing over this lead of the supercap and warm both pieces of tubing with the tip of the soldering iron. They will encase and protect both leads of the supercap and the entire diode.

[  ]  Solder the other end of this 10" red wire to pin 28 of the SmartWatch socket.

[  ]  Using a small screwdriver, pry up the left end of the integrated circuit at socket U208 to provide better access to pin 28 of the IC.

[  ]  Tack solder a 2" length of red wire to the top of pin 28 of this socket. Press this IC back into its socket. This will be the source of needed power to our ZROM.

[  ]  Solder the other end to the extended pin 28 of the ZROM.

[  ]  Review all of the previous steps. There should be no loose wire ends nor missing IC's from their sockets.

[  ]  Leave the video board leaning against the card cage, but ensure it is not shorted by the card cage. Maybe use a sheet of paper between the video board and the card cage.

[  ]  Apply power to the computer and measure the voltage at the SmartWatch socket, pin 28. It should be about +4.7 Vdc, reduced slightly from the normal 5 Vdc because of the voltage drop across the diode. If you are fast, it may be lower and increasing as the supercap is charging.

[  ]  Measure the voltage to the ZROM, pin 28. It should be the computer's normal Vcc, about +5 Vdc.

[  ]  Power down. If successful, the installation is complete. If not, correct the error (diode? or cold solder joint) and repeat.

[  ]  Reassemble the computer and boot-up. Run your clock software as normal, then note the time and shutdown.

[  ]  Leave the computer off for about two hours, then reboot and note the time.


I found that the SmartWatch's clock will remain running for about 1 hour and 45 minutes after power down. Not enough time? Add one or two more supercaps to double or triple the time. Remember to connect them all in parallel, positive to positive and negative to negative.

Call or e-mail if you have any difficulty. Good Luck.

Steven Vagts, Editor, "Z-100 LifeLine"