Forum etiquette

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This forum is part of our mission to promote the preservation of vintage computers through education and outreach. (In real life we also run events and have a museum.) We encourage you to join us, participate, share your knowledge, and enjoy.

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"PM Sent!" messages (or, how to use the Private Message system)

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Copyright and other legal issues

We are here to discuss vintage computing, so discussing software, books, and other intellectual property that is on-topic is fine. We don't want people using these forums to discuss or enable copyright violations or other things that are against the law; whether you agree with the law or not is irrelevant. Do not use our resources for something that is legally or morally questionable.

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New user moderation

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Other suggestions
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Strange problem with APEX 100 after repairing acid damage

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    Strange problem with APEX 100 after repairing acid damage

    A little background:

    I picked up an Epson apex computer that was workign but 12v had shorted and damaged motherboard.

    It booted but there was no 12v power to anything.

    It had significant battery damage to the power connecter area and the 12v power plug had actually burned a small hole in motherboard.

    I spent some time cleaning battery corrosion, fixing damaged traces, re-routing +-12v, and everything checks out except it simply doesn't boot any more!

    So, as I've been troubleshooting the no-boot issue I've noticed that MANY components like resistors, capacitors, and diodes in the general area of the battery seem to simply be completely dead, which I find very mystifying.

    For example, R25 shows correct resistance. R13 - 15 show infinite resisitance. None of the diodes in this area appear to conduct in either direciton; C43 and C44 appear dead, along with several of the tantalum capacitors.

    Once I move past this area and out into the unaffected sections of the board, everything seems to test fine.

    Is this something you've seen before, passive components like resistors and diodes that are VISUALLY fine but simply fail in large numbers like this? Any idea what might be going on? I simply soaked the board in a weak vinegar solution for a litlte while, rinsed thoroughly with isopropyl alcohol, and cleaned traces and whatnot with a fiberglass pencil...
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    Does it boot if you disconnect 12v?


      Also note that a general-purpose diode has to have a voltage in excess of about 0.7V before it will begin to conduct. Right now, I'd suspect your DMM...


        Originally posted by Chuck(G) View Post
        Also note that a general-purpose diode has to have a voltage in excess of about 0.7V before it will begin to conduct. Right now, I'd suspect your DMM...
        Yep the auto-ranging multimeter was completely flaking out. Switched to a selectable range and things look better.

        It does not boot if I disconnect 12v.

        I'm shelving this thing for now, OSC on the isa bus is something like 40mhz according to three different multimeters. It's just wacky as hell. I might dig it back out if I can find a nice budget oscilliscope and poke around on it...