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Thread: Repair of 5160 XT power supply

  1. #1

    Default Repair of 5160 XT power supply

    Hello,

    I have two IBM 5160 from 1985 and 1986 with the 220V "Schrack" 130W supply.
    Both have now output at all voltage-lines. I have testes under load condition with a mainboard, cga, floppy-adapter, two fullsize-floppies.
    If I switch the supply on, at my postcard only the 12V-voltage-LED lights shortly.
    The fans are turning (220V). The fuses are OK. I measured most diodes - they seems to were OK.
    In the supplys are no damages visible.

    Have someone a hint for a typical failure?
    Means the non lighting +5V-LED, that there is the error?
    Has anybody a schematic for this supply? - In the technical reference of the XT is it not!

    thanks and greets
    Christian

  2. #2
    Join Date
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    Default

    Welcome to these forums.

    A common problem with the IBM 5160 is that a tantalum capacitor on the motherboard goes short circuit and overloads the power supply. You can see how common that is by looking at a list of 51xx motherboard failures at [here].

    A procedure for working out which capacitor is faulty is at [here]. Have you tried that?

  3. #3

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    Hi, at one mainboard the C56 had a short circuit and at the other board was a faulty dram-chip.
    I changed these - and now both boards are running great with an working power supply.
    But both original power supplys are not working...

  4. #4

    Default

    +1 on Modem7's site, Follow the minimum diagnostics procedure and report back.

  5. #5

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    Thanks for support, but I tested with this minimum configuration.
    Both mainboards are ok, have no short circuits and works with an other IBM supply from 1984 (made in USA).
    The faulty supplys from Schrack (mde in Europe) have both no voltage on all lines. Only the 220V-fan is turning.
    The supplys are defenitie faulty, but where can I start to search... are there typical errors?
    Last edited by vossi; August 12th, 2015 at 04:03 AM.

  6. #6

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    With the PSU powered up and with nothing connected do you still get 0v on all output lines using a DMM to measure the output voltages ?, Could be Cap failure or a short, these old psu's ain't getting any younger, What tools do you have for troubleshooting. Be extremely careful when working on / inside psu's.

  7. #7

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    I measured the outputs with a dmm under load with the working mainboard. I think I have to check all the caps first...

  8. #8

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    Yes Caps are a likely culprit, Also check the X2 Caps, If they are of the RIFA type replace them while you have the PSU apart.

    Just an aside, Of the 220v Schrack psu's i have, They all power up and output with no load attached due to the load resistors inside albeit not quite optimal, Though i would expect to see in the region of +11 > -11 > +5 > -5 > V with no extra load attached, If the voltages disappear when connecting a known good load it's more than likely cap failure but of course 1 or more Caps could be totally dead hence your 0V output or a short somewhere. Obviously not all psu's are the same.

  9. #9

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    Today I repaired both 5160 supplys
    In both the 3300uF caps at the 7905 regulator had short cirtcuits!
    It's the only cap in the Schrack PSU from this manufactorer - I think it's a bad cap!

    greets
    Christian

  10. #10

    Default

    In the US 5160 supply from '84 are the RIFA time-bombs. They looked not so good - had some cracks. I changed them with new x2-caps.

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