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Thread: Compaq Portable 486 Power Supply Unit

  1. #1

    Question Compaq Portable 486 Power Supply Unit

    Hi all,

    I while ago somebody donated a Compaq Portable 486. On the first try it turned on and started booting Windows 95. Yay!
    But then....

    A loud bang and some smoke! And a dead machine...

    I took it apart and found out that on the Power supply, a few capacitors had exploded along with a VDR and the fuse.
    "No big deal" is what I thought. And it woud have been.
    I desoldered all the bad components, looked them up on-line, wrote everything down and cleaned up the PCB.

    Since I was quite busy at the time, I stored everything in my collection room until I finally had some spare time to order the parts and
    go on with the repair.

    But now I've stumbled upon a problem:

    I forgot the write down where which capacitor should go
    For the major part it is not a problem because I ordered all the parts in exactly the same dimensions as original.
    But there are a few capacitors on the secundary side of the board which i'm afraid to mix up.

    My question to you guys is:

    Does anyone have a schematic diagram or some high-res pictures of this PSU-board?
    Or maybe someone can tell me which values should C23, C27, C28, C44, C63 be?


  2. #2
    Join Date
    Oct 2018
    Fontainebleau, France


    Hello FlaminV,

    I happen to have a Portable 486 right next to me.
    I disassembled the PSU and took some pictures:

    This is not so useful though since the capacitors show their values on the hard-to-see side.
    Here is what I could get:
    C23 = 470F, 25V
    C28 = 1000F, 10V
    C63 = 1000F, 10V

    I could not read C27 and C44 without removing the board, but they read "H9133" on the other side, which is the same as C28 and C63. So, I guess 1000F, 10V.

    Good luck,

  3. #3


    Hi !

    Do you know the pinout for this PSU ? Mine died and i want to do a PicoPSU but i cant find the connector pins output voltages anywhere

    Thanks !

  4. #4


    Ah , by the way :

    C23 = 470uf, 25v
    C27 = 1000uf, 10v
    C28 = 1000uf, 10v
    C44 = 1000uf , 10v
    C63 = 1000uf, 10v
    C31 = 1000uf, 10v
    C24 = 68uf, 35v

    All these caps on my PSU had leaked , so i replaced them all, ive also replaced the screen with a newer 10.4 LED ( very hard to find one that fits on original mount ) ... I was using normally , today, the PSU just dont start, as it had already failed , and the new screen uses far more current than the old CCFL backlit, retrofitting a newer more powerfull one seems to be the case.

  5. #5


    Update on the PSU-fix:

    Thanks to felixzero I managed to solder in all the capacitors on the right places.
    Since then, It has been laying around while I was focussing on other projects.
    Until last week, when I decided it was time to put it to the test.

    The outcome however was unfortunate, Again a loud bang and a tripped breaker this time.
    Upon close inspection it seemed that the newly put in VDR had blown. The problem is, I can't figure out what has caused it to blow.
    Maybe it was the wrong type of VDR?

    To be continued....

    (Thoughts, tips and tricks are welcome)

  6. #6


    Did the VDR have the correct voltage rating? If it's on the primary side, it should probably be a 275V type. The power supply should work without the VDR also - for testing.

  7. #7


    To be honest, I'd have to look it up first. But when I disassembled the PSU and took of all the defect components I ordered new ones with the same specifications. As I recall it was very difficulut to find the matching VDR. I wasn't sure if I could test the PSU without the VDR but if you say so, I'm going to benchtest the PSU (So, outside the actual computer) and measure the voltages on the secundary side.

    To be continued....


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