The board in question was a powered USB hub, the sort that costs about a tenner and powers half my desk. One morning it stopped powering anything, and the sensible response was to buy another one. I did not do the sensible thing. I got the iron out instead, because fixing a thing you can see is far more satisfying than ordering a thing you can't.
The fault announced itself the moment I opened the case: a swollen electrolytic capacitor on the 5V rail, top domed up like a tiny tin of beans that had been left too long. That's the classic failure, and it's almost always the cause when something that used to power up simply doesn't. The capacitor had given up, the rail couldn't hold voltage under load, and the hub was effectively dead.
getting the old one off
Through-hole desoldering with a cheap iron is a small test of patience. I added fresh solder to both joints first, which sounds backwards but works: the new solder remixes with the old and lowers the melting point of the whole blob, so it flows properly instead of staying stubbornly half-set. Then it was the usual dance of heating one leg, rocking the capacitor, heating the other, rocking it back, a fraction at a time until it came free without lifting a pad.
Solder wick cleared the holes. A good pump of flux beforehand makes the wick actually drink the solder rather than just smearing it around, and flux is the single thing most people underuse. It's cheap, it's the difference between a clean joint and a frustrating one, and a flux pen lives permanently on my bench now for exactly this reason.
the new one on
I matched the replacement on three numbers: capacitance, voltage rating, and physical size, in that order of importance. Capacitance has to match, voltage rating you can go up but never down, and a low-ESR part is worth seeking out on a power rail because that's what the original almost certainly was. Polarity matters too, and electrolytics are unforgiving about it: the stripe goes to the negative pad, and getting it backwards turns the capacitor into a small, smelly firework.
Seated, soldered, legs trimmed. Two clean joints, a quick check with a magnifier for bridges, and a wipe of isopropyl to clear the flux residue so I could actually see what I'd done.
Then the moment of truth. Plugged in, the LED came up. A phone on one port started charging, a drive on another spun up and mounted. The hub was alive, and it cost me one capacitor from a drawer of spares and forty minutes I'd happily spend again.
None of this is clever. A bad cap on a power rail is the most ordinary failure there is, and the fix is the most ordinary repair. But there's a particular pleasure in mending something rather than replacing it, in the small refusal to let a tenner of working electronics become landfill over a part worth pennies. The iron pays for itself in feeling, if nothing else.