Unassembling kits

From: Barry A. Watzman <Watzman_at_ibm.net>
Date: Thu Dec 24 11:40:13 1998

I feel like I've been "unassembling" items back into the original kits.

I have recently acquired a variety of old S-100 stuff, very dirty and mostly not working. I spent a lot of time cleaning up an IMSAI, it was really dirty. I disassembled it completely, even removed the motherboard. Cleaned everything completely with flux remover and solvents, and reassembled. Did some troubleshooting and some parts replacement, and have obtained some additional boards from various other people. It now boots CP/M, but only in a very limited way (e.g. it?s a crude BIOS, single drive and console I/O only, minimal, but it works).

I took two Cromemco Z-80 CPU cards, neither working, and removed all of the IC sockets from the boards, then rebuilt the boards with all new sockets and all-new IC?s (I seriously considered soldering the IC?s, but in the end I decided to use new sockets).

The old sockets had a bunch of green corrosion crud inside the contacts (they were TI sockets, which can be removed by prying off the plastic, leaving individual pins soldered to the board, which can then be removed one at a time). Removing the IC sockets was VERY difficult and VERY time consuming, and I did some minor damage to the board traces and pads. I had access to a vacuum desoldering unit at work, but I figured I would remove the sockets and pins first, and then just use the vacuum tool to clear the holes. BIG MISTAKE. The vacuum device works wonders for removing IC?s and IC sockets, but it does NOT do a good job at clearing empty holes. If I?d used it properly, the work would have gone better, with less damage to the boards, and would have taken half the time (e.g. about ten hours instead of about twenty). I know this because when I scrapped a Shugart SA-860 drive for parts, I removed the non-standard IC?s from it?s PC board before pitching it, and that went so much better than the work on the CPU c
ards. The SA-860 was one of four, and now the other three all work.

However, all of that said, both Z-80 CPU boards are now working perfectly as far as I can tell. The system is booting and running at both 2MHz and 4 MHz, and even the front panel works at 4MHz.

I?ve built up an external dual-drive box with two 3.5" 1.44 Mb drives, and an adapter board that makes it connect to a 50-pin cable and look like two 8" drives. The next step will be to get this unit working, which will be quite a bit of work because of many, many software issues. Once I do, I want to transfer everything to 3.5" disks from 8" disks (I have about 500 8" disks full of sofware). This box has a connector on the back for 8" drives, so I can support 4 drives, two 3.5" and two 8".

I?m desperately looking for a Seattle Computer CPU support card, please let me know if you know of anyone who has one.

Barry Watzman

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