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Tips on rebuikding a PC-AT power supply

djfitzgerald

djfitzgerald

Experienced Member
Joined
Dec 28, 2018
Messages
73
Location
Western New England
I was at the last VCF east work weekend last month and the power supply on my 5160 went. One of the guys told me that power supplies were relatively easy to fix, told me the parts that I needed, and said that he would walk me through it the next time we meet. Well, one coronavirus pandemic later it looks like I'll be working from home for the forseeable future and I could use some instruction on how to replace the capacitors in a power supply safely.

Is it as easy as heating up the solider on the old capacitors with my iron, pulling the old one out, putting the new one in, and solidering the new one? What tools will I need? I could use any instruction that folks would be willing to provide me with.

Also, I could use some tips on recommeded places to get capacitors. Here are the parts that I was told I would need to rebuild the power supply:

  • one 470uF @ 16v
  • two 4700uF @ 16v
  • one 2200uF @ 16v
  • one 470uF @ 25v
  • RIFA cap line filters (was told to "use x2 rated saftey caps to replace")
 
Once done replacing the capacitors, you'd need to actually trouble shoot the power supply. It is clearly a good idea to replace the RIFA anyway. As always, I'd recommend finding out what failed first before doing a bulk replacement of capacitors.
The input filter capacitors can have about 330V on them. For safety, always use an isolation transformer. Where insulating shoes. Always put one hand in your pocket. When not measuring something in the high voltage part of the circuit, cover that part with two layers of electrical tape. Use a board holder of some sort ( small bench vice ) so you are not tempted to use two hands.
Dwight
 
Last edited:
Are you sure it is the power supply and not a bad tantalum on the motherboard?

I've never found bad caps in one of these power supplies, but have found a few bad diodes and regulators. Usually the problem is a bad cap on the motherboard or expansion card.
 
It is like a disease. One person makes it work by replacing a bunch of capacitors and it spreads to maybe 10 or 20 others.
None of them, including the original one have no idea how to trouble shoot. Maybe 2 in the 20 actually fix the problem and all follow along.
I often hear "It doesn't do any harm." Of course that isn't always true. A broken trace, a capacitor put in backwards or in this case one with the wrong voltage.
I see he is replacing all the low voltage capacitors but one has to ask why he left out the high voltage input filter caps.
I might ask what equipment the person has to trouble shoot with?
Dwight
 
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