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Thread: SOTA 386SI card in Commodore PC10-III

  1. #1
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    Default SOTA 386SI card in Commodore PC10-III

    I've got a PC10-III a friend gave me eons ago. While moving equipment around I rediscovered it and thought I'd fire it up.

    It has one of those SOTA 386 cards in it, but I cannot get the machine to POST. I recall having a problem with the pins on the 386 socket and having to clean them, which I did again but to no avail. And anyway, I would assume if the 386 weren't working the 8088 on the card would when switched over.

    Anyway, nothing seemed to work. I tried pulling the 386si card, removing the 8088 from it and plugging directly into the mobo. There is a Paradise VGA card in there also (in the first slot on the leftmost side), I tried powering up with it installed and without (connected to composite)... nothing. I'm not sure if there are changes/mods to the mobo made to accomodate the card.

    I was looking at the card earlier and noticed the connector that plugs into the 8088 socket on the mobo is missing pin 1 (ground). Would that be deliberate? It doesn't look like it goes anywhere on the card itself.. the pin seems to be isolated.

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    Question: will a PC10 machine post if the BIOS battery is completely dead? I just clued in that it had one, underneath the bracket for the hard drive.

    I would assume it was dead eons ago, and the machine did periodically start back then. But not at all now.. there's no bios beep or attempt to boot from either drive.

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    Dang.

    I didn't realize the PC 10-III has a clock battery.. tucked under the tray that holds the drives. On inspection it is clear it has leaked. The damage isn't nearly as bad as my Lisa board was but all the same I'm fairly confident we have a couple of bad traces. Whether they are responsible for this situation I don't know though. I'll have to clean up the area and then do some continuity tests
    Really hard to see in the area as the traces are quite small and the solder mask is dark.

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    After claning the board and restoring the traces, if it is still not booting then perhaps turn your attention to the power supply.

    I have a PC 10-II, and although mine is booting, I have a couple of bulging electrolytics in the power supply that need replacing.

    Your supply might not be putting out the correct voltages, stopping the MB from booting?

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    Quote Originally Posted by austfox View Post
    After claning the board and restoring the traces, if it is still not booting then perhaps turn your attention to the power supply.

    I have a PC 10-II, and although mine is booting, I have a couple of bulging electrolytics in the power supply that need replacing.

    Your supply might not be putting out the correct voltages, stopping the MB from booting?
    Yeah I was thinking PSU would be next target. I'm always nervous when I turn it on because I have a few Commodore PCs and the others blew out the RIFA caps on me. Not devastating but not pleasant to go through. But I will test the voltages next for sure once I get this area cleaned up. I remember this computer being a bit hesitant to start in the past. That might be PSU but might also be the traces getting flaky as they were burned by battery acid. There is one small electrolytic cap just to the north of one of the battery posts. The normally silver bit up top is purple.

    I see the legs on several diodes and resistors are also rusty... I don't know if the rust can penetrate into the solder and break the connections between those and the PCB holes they solder into?

    I also found that a 'support leg' on the right side of the case didn't have a screw holding it down to its pass-thru on the motherboard.. it had moved out and scraped the soldermask off two traces and may have been bridging them.

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    I did a voltage test on the 8088 and several TTL chips. I'm getting +4.4V. I'm guessing that's not enough to make things happen, and that I've likely got a problem in the power supply?

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