The computer that Bill Gates himself last wrote software for, the Radio Shack TRS-80 Model 100:
It showed no sign of anything when given power and turned on - as stated in the ad. I left it plugged in for a while, as all the documentation around this guy says the internal battery needs a decent charge for the display to function 100%. This didn't make a different though (not suprising when you see below). This thing was cosmetically almost perfect. No yellowing or scratches - thats a good start. Better yet it came with this guy:
A "SuperROM" expansion rom (more on this in a future blog post). Unfortunately this is were the good news finishes. I opened it up to see what I was dealing with:
I was greeted with a pretty acidic smell and corrosion pretty much everywhere! I haven't seen something this bad in person before. Take a look at the ribbon cable connector for the LCD:
Most of the electrolytic capacitors had let go too:
I removed all of capacitors that had let go:
I then cleaned up the board as best I could:
And replaced all of the capacitors. Unfortunately it made no difference. No sign of life on the display. I used the troubleshooting guide (and stopped taking pictures - sorry!), which said start with metering the various voltages put out by the power supply. None of these were right! I cheated and instead of trying to diagnose any supply issues, I used my bench supply to provide the various required voltages - unfortunately this too made no difference either. Every different output i tried to measure, from just checking voltages supplied to chips, to reset lines, data lines and everything in between. Nothing.
This was just before Christmas. I left all of this to sit on the bench for a bit while I enjoyed some time with family and friends away from screens of any sort. At the start of January I had another crack at the board - but couldn't get it to show any signs of life anywhere. So while I continued to play, I kept looking online to see if I could find another unit that might have a better chance of being brought back to life. I was lucky enough to find exactly what I was looking for - a unit in "average" cosmetic condition, but in working condition going for a lot less than these things commonly go for - and so I bought it.
This is the first time I have "given up" and not been able to fix something. This annoyed me a little - but is also a risk you take buying 30+ year old electronics online. I waited for the second unit to arrive, and got straight to work when it did:
It was quite yellow (more so than shows in the picture above), it had a rattle when I moved it and it also wasn't screwed shut. However - it worked! The display wasn't great but I could see what I was supposed to when I powered this guy up - thats a good start! I took a breath and opened it up to see what this unit might hold. I wasn't super excited when I took the four case screws out and one of the four was obviously a replacement - and a poor one at that:
The board looked pretty good (I guess anything wold compared to the last unit):
I then discovered what the rattle was, and why the case didn't seem to be screwed shut despite having all four case screws done up tight - two of the stand offs on the bottom of the top half of the case had snapped off and were rolling around inside the case (bottom two corners):
This is what I found rolling around inside:
Looking around for signs of corrosion I didn't see much at all. The battery looked like it had just started to let go - lucky! So out it came:
There was a small amount of corrosion on the board - but nothing that didn't clean right off with some isopropyl alcohol:
I put a new battery in, and then had a look at the capacitors. I couldn't see much - but thought for the small cost of recapping why not rip them out - I'm glad I did:
Most of the ones I pulled out showed signs of letting go like those above. Again I think i got super lucky and caught these ones just in time! There are a couple of larger capacitors I didn't have replacements for - so I will come back and replace them in the near future. From here I decided to take a look around the board more generally. The DB25 RS232 port on this guy was pretty gross - I don't know what the previous owner had done to it. The installed RAM expansions also stood out a little:
So since I now have a spare - I thought why not switch them out? So that's what I did. I removed the DB25 and soldered RAM from the non-working unit:
I had to remove the DB25 from the working unit, the RAM expansions though are socketed - so just needed to be removed (no de-soldering required). Once that was done I installed the replacement parts and put the board back in the case from the non-working unit (that was in fantastic condition):
I swapped the LCD from the working unit into the non-working units case (given the corrosion you saw on the connector alone above) and took the keyboard out and gave it a good once over. At that point I put the whole thing together. Low and behold - my new working 32K TRS-80 Model 100 computer:
I've got a few things to try with this guy now that it's working - but that will be the topic of another blog post some time soon I hope.
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