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Thread: scored a nice apple IIe need help fixing

  1. #1
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    Default scored a nice apple IIe need help fixing

    Hi guys, scored a nice apple IIe for like 5 usd.
    The unit is non working hooking a composite monitor gives only a black screen.
    The power supply starts and the power led turn red on the motherboard.

    any tips on how to debug this kind of issue on the apple IIe ?

    Thanks!

  2. #2
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    What test gear do you have? Oscilloscope or logic probe?

  3. #3
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    Have you tried the self test?

    Hold closed Apple and turn the power on. Or hold down both Apples and power on. Or disconnect the keyboard and power on.

  4. #4
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    Tried it but do nothing black screen resocket all ICs, tested the power supply voltages and seem ok.
    The charter rom have a missing leg soldered a pice of wire to it as replacement but black screen anyways.
    I have a 5 mhz osciloscope and a logic probe. Poked arround the cpu pins using the logic probe but all of them are stuck in hi or low seems to be no activity on it.

  5. #5
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    There's a rare chance you could have a dead 65c02. I think RAM problems are more likely, but usually with a RAM problem, the computer will do something.

    I think a dead custom chip is the most likely in this case, but you may have a more simple traditional problem like bad reset circuit or clock.

    Since you have a chip with a missing pin, that makes me suspicious about the history of this computer. It may have multiple problems.

    But since my memory of //e diagnostic and repair is not what it yoostsaby, I'll quietly step in the background.

    (Although if you're sure none of the processor pins have pulses, you probably do have a dead clock generator. Or a shorted chip stopping the clock. You could remove all the socketed chips and probe the clock line to check for that. It may be as simple as a corroded 65c02 socket.)

  6. #6
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    Given that you have no video the fault is unlikely to be the CPU, RAM or a reset issue.

    I'd start by looking at the clock circuit.

    A quick test you can do with a multimeter is to ensure that +12v actually makes it to the board. Over the years I've come across more than a few with a loose power connector. The clock circuit requires +12v to operate.
    Last edited by David_M; January 12th, 2018 at 02:13 PM.

  7. #7
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    +12 goes fine into the motherboard replaced the psu for a known good one that got from another apple II.
    I'm really lost on how the clock circuit should work

  8. #8
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    I seem to recall that Sam's service documentation is freely available for these online somewhere (sorry can't really search for it right now). With that you could start by making sure the +12 and ground are actually present at the clock generator. And then you could check for clock pulses.
    Be polite and I may let you live.

  9. #9
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    Thanks found the guide and seems to be just what i need

  10. #10
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    Check pin 11 of the 74ls125 with your logic probe it should be pulsing at 14MHz, if its not check pin 13 is low. Pin 13 is the enable line for the gate and it has a 1k pulldown resistor on the board. If pin 13 looks good then check the input to the gate on pin 12, that is fed directly by the oscillator circuit.

    If the 74ls 125 looks good then its mostly the HAL or its socket that is faulty.

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