I was asked by a friend to attempt a repair on an Acbel power supply from an old Apple Mac. He had highlighted some useful tips for repair from the Web that I have included here. It is a complex (to me, anyway) switch-mode power supply. I could not find a circuit. The received wisdom, mainly from the "badcaps" website, is that these power supplies are robust and usually repairable by replacing electrolytic caps, but which one?
https://www.badcaps.net/forum/showthread.php?t=25253 . I decided to extract the list of most likely suspects and test them one by one using my analogue Avo. The first two checked out OK - slow charge to a resistance exceeding 1M and retention of charge for a long time, depending on capacitance. The board is packed with components and heat is evidently a problem as witnessed by the use of 2 cooling fans. Eventually I picked on C60, a 1000uF 10v 105C cap made by Teapo. The PDF attachment shows its location in a group of 4 electrolytics glued together with potting compound above the upper large aluminium heatsink. Close inspection showed the top of the can was very slightly bulged. It had lost most of its capacitance since it charged almost instantaneously and discharged within 2 seconds. I looked for a replacement with greater that 105C spec but since the original was merely 8mm diameter I could not find a higher spec component that was less than 10mm. Even a 10mm item wouldn't easily fit in the space available. I could maybe have shoe-horned one it but it would have been touching 2 adjacent high wattage resistors that were no doubt producing heat and therefore would have defeated the object. I rejected using extender leads owing to the risk of introducing instability. Having replaced the cap with a Panasonic component I needed to understand how to power up the PSU on the bench, since I didn't have the Apple Mac to go with it. This link was incredibly helpful because it shows all the pin-outs and the fact that 2 sets of pins needed bridging, one with a 10-30 Ohm resistor to defeat the 3.3v sense:
http://haertle.ch/tinker/ps/ Thankfully, all went well, the PSU powered up, and I got all of the expected outputs. The PSU hasn't been refitted to the computer yet, and so I am tempting fate by posting a success story but, hopefully, installed performance will be OK. Cheers, Jerry