VOGONS


First post, by TSteege

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Needing some help. I have a dead Tandy 2100 Model 10 and have been trying for some time to revive it. I purchased new power supply thinking that was the issue but it is not. When I plug P9 into the motherboard, the fan on the PS spins and the motherboard will beep, but when I plug the P8 either alone or with the P9 it does absolutely nothing. I have removed all cards and memory but to no avail. I removed the MB and visually I can not see any dark spots or rust, so I am asking to see if anyone here has a place I should start looking as far as voltage points or impedance tests I should perform. Thank you in advance to anyone with suggestions.

Reply 1 of 9, by snufkin

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Short on one of the pins on P8 to another? Assuming the pinout is the same as an AT supply, check the resistance on the motherboard P8 connector between pin 3 (+12V) & 6 (GND), and 4 (-12V) & 6. Any pictures of the motherboard?

Reply 2 of 9, by TSteege

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Well I added the fix by adding a 3v button battery to the RTC, but to no avail. She still won't work.

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Reply 4 of 9, by snufkin

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If the PSU fan spins up when P8 is disconnected, but doesn't spin up with P8 is connected, then there's a chance that the PSU is detecting a short on either the +12V (yellow) or -12V (blue). I'd disconnect P8, then on the motherboard measure the resistance between pin 3 (where the yellow wire connects) and pin 6 (where one of the black cables connect), then between pin 4 (where the blue wire connects) and pin 6. It's possible that one of the tantalum capacitors has failed short (maybe one of those C11-C14) and needs replacing.

Reply 6 of 9, by TSteege

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snufkin wrote on 2021-09-20, 10:26:

If the PSU fan spins up when P8 is disconnected, but doesn't spin up with P8 is connected, then there's a chance that the PSU is detecting a short on either the +12V (yellow) or -12V (blue). I'd disconnect P8, then on the motherboard measure the resistance between pin 3 (where the yellow wire connects) and pin 6 (where one of the black cables connect), then between pin 4 (where the blue wire connects) and pin 6. It's possible that one of the tantalum capacitors has failed short (maybe one of those C11-C14) and needs replacing.

Finally got back to this project. The resistance from pin 3 to pin 6 is 0, and between 4 to 6 is does seem to be working. I will see about getting some replacement caps.

When I check ohms on each of the caps you talked about. One reads 0 so I am thinking it is the dead one. I do not know what to order, it reads 106 and below that reads +16K. I really appreciate all your help!

Thank you again!

Reply 9 of 9, by TSteege

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SUCCESS!!! I was able to use the new "hack" I did on the Dallas Realtime Clock and changed out one of the 10uF capacitors and it LIVES! Thank you again to everyone, especially @Snufkin here on Vogons.org. Now to get the HD to boot, I think it is dead, but I do have a spare IDE that should work. Thanks again, everyone!

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