TRS-80 Model 102 - Page 1
Forum section: electronics / general

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 19, 2018, 01:45:06 am
content: Got it today, took it apart. Battery leak juice got in there pretty good, there's green moss in many places. Oh well.OOoohhkay, here's some pics. The 4 AA cells are in a plastic holder. Once the holder removed, the dried remains of battery juice under the holder are evident, clearly it also osmosed through the PCB vias to end up on some circuitry, where over the years it patiently chewed away at stuff.Great.Also, one single pin on a SRAM all the way on the other end of the PCB has green fuzzies on it. Weird. I'm thinking it needs replacing because how can I be sure there isn't more green moss waiting to chew its way into the package?I guess vinegar and the old 0000 steel wool will clean up the PCB nicely exposing which traces will need jumpering. I suppose the bunch of chips will need to be replaced. I've never seen packages like this except in old stuff, sort of very rectangular SOIC packages. Interesting.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 20, 2018, 06:16:02 am
content: The green junk makes the chips just pop off the PCB. Gonna be fun cleaning this up. Plus I probably need to jumper all the vias in that area....

author: rrinker
author_rank: Super Contributor
timestamp: October 22, 2018, 02:01:49 pm
content: Good luck.I was give a Model 100. I wasn't going to tear it open as I put batteries in it (previous owner was pretty smart about that sort of thing - didn't leave batteries in when it got stored away) and it worked perfectly. But then curiosity got the better of me so I opened it up. Good thing I did - the NiCad battery for memory backup was JUST starting to leak - the damage didn't extend past the pin on the battery itself. For now I just removed it, so if I replace the AA's the memory is gone, but I just play around with it a little anyway so no big deal.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 25, 2018, 06:05:01 am
content: Hirose still makes the 25 pin connector used for the serial port, I simply removed the metal shell on the new one and reused the old screws so it looks the same as original.!Then I removed some of the worst corroded 0805 resistors and cleaned up the pads with fresh braid. After a few cycles of flux remover and alcohol everything looks new.Will remove the other corroded parts and will try to add new parts soon.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 26, 2018, 12:46:21 am
content: I continued the "debriding" of corroded parts. I was wondering how come these resistors had corroded joints with no obvious path for battery juice; the answer is simple. They used via-in-pad on some of the resistors. Also explains the blobby solder joints overall, too much solder. Now I know why.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 26, 2018, 01:15:53 am
content: I haven't opened my 102 yet, but my model 100 was starting to see corrosion by the smaller electrolytic capacitors - I ended up replacing all of them. The NiCd was also swollen and I got it replaced by a similar one. Otherwise, these computers are quite well designed and manufactured. Good luck in your cleanup!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 26, 2018, 03:23:16 am
content: LOL 1206 parts, not 0805...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 04, 2018, 02:19:45 am
content: I've sanded down the damaged part of the board down to the copper. ~50% of the traces including vias are open circuit because of various sized pits along the trace and what I think are empty vias.The corrosion has even made it outside the computer. The 40 pin system bus expansion connector has grey powder on the PCB pins but when I look into the pins that face outside they are green inside.Amazing. I'd say about 20 wires will need to be soldered in as well as the 50-60 parts I removed.