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TRS-80 Model 100 worked great, suddenly won't turn on.

nerdhouse

nerdhouse

Member
Joined
May 11, 2022
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40
Location
WA
Hi all!

I recently acquired a TRS-80 Model 100 and have been using it for a day or so on battery and it was working great.

When I turned it on this evening, the screen seemed to be dimming a bit when it was plugged into serial, so I unplugged it and used it for a while messing around with BASIC.

30 minutes later or so, there was some corruption on the screen. A power cycle caused the corruption to be even weirder, and now the device won't turn on at all anymore. At first I thought the AAs were just dead, but I've since tried three different sets of batteries and it still won't come on. Sometimes when I flick the power switch, there are some lines on the screen, and then it immediately goes blank again.

Could this have something to do with the internal battery? I'm not sure how it works.

Otherwise I could go poking around for bad caps or something. I kinda assume it hasn't been used since at least the 90's until recently, and then I used it for a bunch of hours all at once.

Any advice on where to start looking would be appreciated.
 
The internal battery is only there to keep the memory alive while changing the main batteries. Most people remove it entirely as its prone to leaking but a 5v 1F supercapacitor works well to replace it.
Also yes, capacitors are a known issue with the model 100. If you have not already done so you should get that checked.
 
i don't have a multimeter, so i can't check everything, but none of the caps seem to be bulging, or leaking, and nothing smells bad. the thing seems basically brand new. the battery isn't leaking or anything eithr. it could be capacitors, but i'd be pretty surprised.

just before it stopped working, i turned it off, took out a single battery, and put it back in to see if the backup battery was still good. it was.

shortly after that the screen had some slight corruption on it.

i guess i'll have to cave and finally buy a multimeter.
 
Nope. They do go bad.
Mine was stone dead when I got it and the caps passed visual. They all failed on ESR. The leakage appeared only after I began removing those itty bitty caps.
 
Seems like the issue was related to the backup battery. I left some AAs in overnight, and it turns on fine now.

I have a feeling that the battery's charge drained quickly when I removed the AAs. Seems like the device won't turn on at all if the "memory power" switch is off, and I have a feeling that a dead battery would cause the same thing to happen.

Guess a replacement battery (or super capacitor) is in my future.
 
If you have not yet replaced the backup battery, at least remove it. The Model 100 will work without it. But of course it will not retain its memory content when powered off.
As already mentioned by NeXT, there is a serious risk of leaking when the back-up battery ages. The acid will destroy the motherboard!
 
LaserVision said:
If you have not yet replaced the backup battery, at least remove it. The Model 100 will work without it. But of course it will not retain its memory content when powered off.
As already mentioned by NeXT, there is a serious risk of leaking when the back-up battery ages. The acid will destroy the motherboard!
Click to expand...
don't worry, i just ordered a replacement battery, and checked the condition a few days ago. it's looking a bit crusty, but everything is totally fine for now and it will likely get replaced this weekend if my batteries arrive. thanks for your concern.
 
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