Help with PCjr Power Supply Board

[gobabushka]

I just got a PCjr from a friend that I'm hoping to put back into service. It won't power up, so I pulled out the multimeter and checked the PSU board in the machine, looks like the 12v rail is only putting out round 8. any suggestions on where to start?

 

[hargle]

I can't really help with the debugging, and this may not really be helpful at all, but I have a spare power supply card from inside a sidecar that I have no use for. I'd be happy to send it to you for shipping. This offer is just for the internal PCB, no sidecar shell and no power brick.
It may be useful for stealing caps or other bits from.

 

[mechanizeddeath]

I really, really wish I could help. If I could somehow contact my 13 year old self I'm sure he/I would have the answer. That was the age I found a cache of PCjr machines in a storage closet at my Jr High. I repaired and rebuilt nearly every one of them for my English teacher to use for a makeshift writing lab. I know I fixed a few power supply issues.

I seem to remember a few obviously blown caps, but if you own a multimeter and know how to use it, those would have already been apparent.

 

[gobabushka]

could you send me a pic of the board, I cant find one. Thanks!

 

[Trixter]

Have you tried looking at the PCjr Tech Reference? It might have power supply diagrams and expected inputs/outputs but I don't recall from memory. The PCjr tech ref appears to be online here: http://www.retroarchive.org/dos/docs/index.html

 

[Chuck(G)]

The big TO-3 device on the board is a 7812, +12V regulator. Measure the voltage between the case and each of the two pins. One should read about +17V.

http://www.mikrocontroller.net/attachment/97748/78XX_05_12_15.pdf

 

[gobabushka]

Well, it looks like the power supply is ok, but there is some corrosion on the rightmost cartridge port.

I actually started a new thread for it.

http://www.vintage-computer.com/vcforum/showthread.php?35148-PCjr-white-screen-solid-*buzz*-from-speaker