by Richard F. Drushel (drushel@apk.net)
Thank you for your patience...it's been since 17 November 1997 that I have produced a TWWMCA. My end-of-semester teaching crunch hit about then, and didn't let up until Christmas; but I had let so many things slip at home that I used Christmas Break for them. And of course, the start of the spring semester has its own crunch. Now that all the plates are spinning again (like the juggler at the circus), I have some space in my schedule again for TWWMCA.
A local computer junkie, Fred Horvat (some of you may remember him from his brief stopover at ADAMcon IV), had some ADAM pieces and parts which he said were nonfunctional, taking up space, and needed to be moved somewhere... pack rat that I am, I told him I'd take what he had and see what I could do with it. Since he lives way on the west side of Cleveland, and I live on the east side, we decided to meet at a "neutral site" (a Blockbuster Video store he passes on his way home from work in Akron) for the pickup.
When I met Fred, it turned out he hadn't been able to find all the stuff he wanted to get rid of--only a couple of ADAM system units. Perhaps as some compensation, he brought me a working original IBM-PC system (the one with the cassette port, not the later XT) and color monitor. Welcome to 1981 :-) but I can put it to good use--each of my 4 daughters now has her own computer.
The ADAM system units were a bit dirty, and one was missing the lid covering the 3 expansion slots. Each had one tape drive and one of the all- plastic type of drive bay placeholders (as opposed to the earlier kind which had a metal frame). There were no major scuffs or scratches, but one of the system units had a half-inch hole in it around the disk drive ADAMnet port.
Standard operating procedure for me with new-found ADAMs (reported to be working or not) is to completely disassemble them, clean them up, then test them under power. A few minutes with a Phillips-head screwdriver took care of the disassembly part. The plastic case pieces were put into a laundry tub full of hot water and Tide detergent. The metal shielding was intact on one system unit, missing except for the bottom memory board shield on the other. They weren't very corroded (sometimes they get quite rusty), but had lots of dust, so I threw them into the detergent as well.
For those of you who've never been inside an ADAM, there are two circuit boards: a rectangular "memory board" on the bottom, and a square "video board" on top. The memory board has the 64K of RAM, the EOS and SmartWriter ROMs. the 3 internal expansion slots, the sideport expansion connector, the tape drive connectors, and the ADAMnet master 6801 microcontroller. The video board has the video circuitry, the Z80 microprocessor, the ColecoVision OS-7 ROM, the game controller connectors, and the game cartridge slot. The video board is actually just a modified version of the ColecoVision video game board; the Expansion Module 3 version of the ADAM (which connects to a ColecoVision) has just the memory board. In the ADAM, there is a ribbon cable with edgecard connector between the memory and video boards.
The circuit boards of both system units were revision D1-D3; PROMs (no version labels) instead of EPROMS; 3-ROM configuration (8K EOS, 8K and 16K SmartWriter) instead of 4-ROM (8K EOS, 3 x 8K SmartWriter); master and tape 6801s socketed; memory I/O controller soldered; lots of rework on the memory board (extra jumpers, capacitors, cut traces). Based upon this, I expected to find R80 SmartWriter when (if) the machines were booted.
There was one surprise inside the system unit which had the hole in the case--a complete mouse nest made of pink fiberglass insulation! This and other goodies were stuffed into the space between the outside of the case and the back wall of the internal expansion bay. The case plastic is about a quarter inch thick; I can't imagine some rodent chewing away at that for very long...but I don't know how else to interpret it. My daughters were pretty grossed out when I showed them the nest.
The cases cleaned up nicely in the detergent. Sometimes you will find old stickum from labels which have fallen off, or from tape, which the detergent won't remove. For this, I use lighter fluid (naphtha) and paper towels. If the case is badly discolored (too long under fluorescent lights, or else owned by a smoker), there's not much you can do. I have read reports that Formula 409 stain remover plus one of those green Scotchbrite pot scrubbers can remove this kind of heavy staining (at the expense of the finish), but I've never tried it myself.
Finally, I was able to put the circuit boards back in (minus all the shielding) for the first powered tests. The first system booted right away, with good video. The second system had a scrambled screen, and the printer didn't give the normal carriage return/line feed expected when booting into the Electronic Typewriter. So, which board was bad--the memory board or the video board? I decided to do a swap test using the first system unit; clearly it had 2 good boards. Memory board 1 plus video board 2 --> system worked! So, it must be a bad memory board. However, the reciprocal test of memory board 2 plus video board 1 also worked! This suggested a dirty edgecard connector on the ribbon cable between the memory and video boards. Cleaning the traces with a pencil eraser and reseating the connector a few time cured the problem.
You might be thinking that it's dangerous to troubleshoot by swapping--isn't it possible that a bad board will damage a good board, leaving you with a stack of blown boards? Yes, it is possible. My experience has been, however, that as long as the boards don't have dead short circuits in them (i.e., a direct connection between supply voltage and ground), there isn't much real danger. Shorted boards can be identified by the presence of burned traces, burned wires, or literally blown/fried chips. Such a board must have any damaged components removed and replaced, and the source of the short identified and fixed, before applying power. Component-level troubleshooting is best left to experts.
Now that I was sure both systems worked electrically, I put everything back together properly, including all the shielding. For the system which was missing most of the shielding, I went to my ADAM junkbox and got the necessary pieces. I tested both systems again after the shielding was installed, but before the cover was screwed down, just to make sure I didn't have any loose connections--it's really annoying to keep unscrewing the case more than a few times in one sitting :-)
The last items to test were the tape drives. Plug them in, put in a tape (my Donkey Kong Super Game was the closest at hand), pull the reset switch, and pray...luckily, both drives booted successfully.
So, for the cost of a scoop of detergent and an afternoon's time, I was able to add two more ADAM system units to my collection. I have found many times, with many different kinds of machinery, that simple disassembly, cleaning, and reassembly resurrects many "dead" items. Remember this the next time your ADAM flakes out.
I have some ADAM schematic diagrams in .GIF format. They aren't scans of Coleco schematics; I redid them using Canvas 3.5 graphics software, so they are neat and legible :-). I will put these up for download and talk about them next time.
See you again next week!
*Rich*
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