A power supply in one of my desktop boxes died this week. Not dramatically, no bang, no smoke, just a machine that would no longer power on and a faint, unhealthy ticking when I pressed the button. The sensible, modern thing to do is to bin it and buy a new one. They are cheap. My time is not free. By every rational measure I should have ordered a replacement and moved on.
I opened it instead, because of course I did.
Safety first, and I mean it. A PSU has large capacitors that hold a genuinely dangerous charge long after it is unplugged. This is not the place for bravado. I unplugged it, left it overnight, and discharged the primary capacitor through a resistor before I let my fingers anywhere near the board. If you are not comfortable with that sentence, do not open a PSU. The low-voltage hobby stuff is forgiving. Mains-side electronics is not.
With the lid off, the fault announced itself immediately. Three electrolytic capacitors on the secondary side, the low-voltage output stage, were visibly bulging. The tops had domed up where they should be flat, and one had the faint crusty residue of an electrolyte that had decided to leave. This is the single most common failure in cheap-to-midrange PSUs, and it is gloriously fixable.
I noted the values off the casings, 1000µF 10V and a couple of 470µF 16V, and ordered replacements rated at 105°C rather than the 85°C parts that had failed. The higher temperature rating costs pennies more and lasts considerably longer in the warm, badly-ventilated guts of a PSU. The whole order came to a couple of pounds.
The desoldering was the only fiddly part. Through-hole electrolytics on a board with a decent ground plane suck the heat away from your iron, so you need a hot tip and patience, working the joint and the solder sucker together until the leg comes free without lifting a pad. Fitting the new ones the right way round matters: electrolytics are polarised, and putting one in backwards is how you turn a quiet repair into the bang I was relieved to have avoided earlier. The board marks the negative side, the capacitor marks it too, line them up.
Reassembled, plugged into a spare load rather than my actual machine for the first test (I am cautious, not reckless), it powered up clean. Steady rails, no ticking, the fan spinning up as it should. Back in the desktop it has run without complaint for three days now.
Was it worth it? Strictly economically, no. The capacitors cost less than the replacement PSU would have, but my evening was worth more than the difference, and a rational person would call that a loss. But I do not really do this for the economics. I do it because a thing that was destined for landfill is now sat in a working computer, because I understand exactly what failed and why, and because there is a specific small joy in fixing something with your own hands that no amount of one-click ordering will ever replace. The new one would have been better. This one is mine.