A power supply died on one of my older boxes this week, and rather than do the sensible modern thing and order a new one, I opened it up. I'm glad I did, because the fault was about as textbook as faults get, and the fix cost me less than a coffee.
The symptom was a machine that wouldn't power on. Fans gave a single twitch and then nothing, no POST, no beep, dead. The motherboard was getting standby power, the little light was on, but pressing the button just produced that hopeful twitch and silence. Classic ATX power supply behaviour when it can't hold its rails up under load. Before condemning the board I wanted to rule out the PSU, so out came the screwdriver.
You have to be a bit careful here. The big primary-side capacitors in a power supply store a serious charge and can hold it long after it's unplugged, enough to give you a proper unpleasant surprise. I left it unplugged for a good while and discharged the large caps through a resistor before poking around. With that done, the fault was visible the moment I had the lid off. Two of the electrolytic capacitors on the secondary side, the low-voltage output side, had bulged tops. Where they should be flat, they were domed, and one had a faint crust of dried electrolyte around the vent. Bad caps. The plague that took out a generation of hardware in the mid-2000s, still claiming victims a decade on.
Bulged capacitors are one of the most repairable faults in consumer electronics, because the failure is mechanical and obvious and the parts are pennies. I noted the values printed on the side, the capacitance in microfarads and the voltage rating, and ordered replacements rated for 105°C, which is what you want for anything sitting in the warm guts of a PSU. Low-ESR types, to match what they replace. Total cost, about four quid for a small bag of them with spares.
The actual swap is the fiddly bit, and not because the soldering is hard. It's that power supply boards have big ground planes that suck heat away from the joint, so a small iron just won't get the pad hot enough to flow. You sit there melting nothing while the board acts as a giant heatsink. I cranked the iron up, added a bit of fresh solder to the old joint to help it flow, and used desoldering braid to clear the holes once the leads were out. New caps in, watching the polarity, because electrolytics go in one way round and the other way round they vent dramatically. Stripe to the marked side. Solder, snip the leads, done.
It powered up first try. The machine POSTed, booted, and has been running steadily since. The whole repair took half an hour and four pounds, against the cost and the landfill of a whole replacement unit.
I'm not going to pretend every dead PSU is worth saving. If the primary side has let go, or there's scorching around the switching transistors, bin it and don't think twice, it's not worth your time or the risk. But bulged secondary caps are the easy win, the fault that rewards anyone willing to open the case and look. We throw away an enormous amount of hardware that wants nothing more than a fiver of capacitors and twenty minutes with an iron. Worth a look before it goes in the skip.