Restoration of a Zenith/Heathkit Z-100

I recently acquired a Zenith/Heathkit Z-100. I almost didn't buy it because I have a number of S-100 bus systems, including an Intel 8080. But I was curious about its "dual processor" capabilities. So pack-rat that I am, I bought it. Here's the process I followed in my restoration: I checked out Herb Johnson's website which has a lot of good information on this system (http://www.retrotechnology.com/herbs_stuff/z100.html). I especially checked out his description of how to strip a Z-100 down to its motherboard (http://www.retrotechnology.com/restore/z_repair.html). I did just that - removed the floppy disk and hard disk unit from the Z-100. I then removed the outer case and keyboard. Next came the video board. I also removed the Floppy Disk controller and the Hard Disk controller from the S-100 bus on the motherboard. Next I disconnected the power connections from the motherboard and removed the keyboard and found the foam mounting material gooey and disintegrating (not unusual for vintage systems). Finally I removed the video controller from the motherboard. Stripping the system gave me the opportunity to check out the motherboard - both in terms of integrity and making sure that all the chips (which are socketed) were seated correctly. It also allowed me to document all of the jumper and switch settings on the motherboard. I found that the motherboard had been upgraded to the full 786KB of RAM. I examined the video daughter card - and found it had the full 64K of video RAM. I also found that the motherboard had been upgraded with a "UCI - ZSM 8Mhz" daughter card. I also noted that U146 had been modified with a 74L257 "stacked" on top of whatever chip was originally there. I have no Idea what that was for (if any of you do, please let me know!). I cleaned up the gooey foam and installed some Scotch two sided foam to replace it. I then put a dummy load on the power supply (switching supplies "like" loads). I used an old disk drive for the load (which I didn't care if it got destroyed by an aberrant voltage). I powered the system on - and the disk drive came up normally. I checked out all the power supply voltages: +16 was +15.98; +8 was +7.75; -16 was -16; +5 was +5.01 with 2mv of AC; +12 was 11.82 with 7mv of AC. Given these good readings, I was ready to re-install all the systems components - which I did. (BTW, while I was disassembling the system, I had made extensive notes on what cables went where, etc., so putting it back together was an easy task.) I then cleaned the contacts of the S-100 Floppy Disk Controller and Hard Disk Controller with DeoxIT Gold (formerly ProGold). I've found the stuff is terrific in making sure contacts have great conductivity - and stay that way. I then re-inserted both into the S-100 bus. I connected a video monitor to the system - turned it on - and then powered up the system. To my great (and pleasant) surprise, the screen indicated that the system tried to boot but found a hardware problem. Fortunately, the system's ROM has a number of built-in diagnostics. The "startup" diags passed, as did the memory and keyboard. However, the HDD could not be read. Before I jumped to the conclusion that the HDD was bad (it was spinning happily) - I decided to re-check my re-cabling. Sure enough, I had forgot to re-attach a power connector to the HDD separator board. After fixing my goof, I power up the system again - and to my super pleasure, it booted up to a prompt! I had hoped it would be CP/M - but instead it was Zenith DOS 2.11. I've played with the system a bit - including testing out the floppy disk drive - and backing up the DOS system. Everything seems to work well. Here's the Z-100's hardware configuration: Dual CPU 8085, 8088 RAM 768K Video RAM 64K, Color HDD 10MB FDD 320K (double side, dual density) 8MHz upgrade Cheers, Lyle -- Lyle Bickley, AF6WS Bickley Consulting West Inc. http://bickleywest.com "Black holes are where God is dividing by zero"