Compaq Portable (1) Power Supply shorted, need help with repair and/or replacement

[Nevets01]

the PSU in my Compaq Portable (pictures attached) is shorted, and has blown two fuses already.
Obviously I would love to rectify this.
I have already tried the lamp-in-series trick, which confirms a short (lamp lights up just as brightly as it normally would).
None of the capacitors appear bad, either to my eyes or my voltmeter.
I have attempted this detached from the computer, and isolated the PSU as the problem (though the motherboard also might have problems, I can't really figure that out until I get this sorted)
I have attempted to connect a standard ATX power supply to the thing, but am confounded by the nonstandard lines "+5vR" (I'm guessing '5v return', for voltage regulation), "PC" (??), and "+5v" (seems to be the other leg of a cap which is connected to the normal 5v rail).
Schematics or proper documentation seems scant to nonexistent for these parts; the service manual provides little enlightenment (simply advising to "replace PSU" for this sort of problem, and no mention of how the thing works other than a listing of voltage ratings) and I am unable to find even a circuit diagram.
Advice or help would be appreciated in getting this board to work again, or in acquiring/constructing a replacement
Thank you
-Nevets01

 

[VERAULT]

are you sure its the PSU and not one or more burnt tantalum capacitors on the mainboard?

 

[Nevets01]

are you sure its the PSU and not one or more burnt tantalum capacitors on the mainboard?

Yes. I have checked the PSU while it is COMPLETELY disconnected from the computer; same result.

 

[Hugo Holden]

It looks like a well made supply to me and worth fixing. It is worth checking all the diodes and transistors, most of which you can do in circuit, looking for shorts, since its blowing fuses, so it is likely a diode or transistor or another component has failed short circuit, that is if the fault resides on the supply board and not on the computer board.

Often there is scant information on some computer supplies. But actually, it is all there right in front of you, just not in a convenient form. You can, if you are patient, copy out the schematic and figure out from that what voltages you would expect where. I did this for the IBM-5155 supply. It is a lot of work, but once you have done it , it will help you as long as you own it and help others too if you publish your findings.

 

[iz8dwf]

Hello,
dead shorts on AC side of SMPSUs are usually due to shorted bridge diode(s), and/or shorted BJT/Mosfet on the primary transformer side or less likely shorted capacitors after the rectifier.
It usually can't be a problem on the secondary side because that would probably trigger the overcurrent protection and shutdown the primary side PWM (the SMPSU usually goes "ticking" when there's a short on the secondary side).
HTH
Frank IZ8DWF

 

[SpidersWeb]

In my Compaq Portable, I found tantalum caps that had shorted inside the supply itself. Check those also.