The board was dead. No power light, no fan twitch, nothing. The kind of dead where you press the button a few more times as if persistence is a diagnostic technique. It is not, but I did it anyway.
I nearly binned it. The honest cost-benefit here is poor: my time is worth more than the board, and a replacement was thirty quid. But there's a particular itch that a dead board scratches at, and it isn't really about the thirty quid. It's that I wanted to know why. A thing that worked yesterday and not today has a reason, and the reason is sitting right there on the PCB waiting to be found.
looking before touching
First rule, and the one I most often ignore in my impatience: look before you reach for the iron. Most board failures announce themselves visually if you give them a chance. So I got it under a bright light with a loupe and went over it slowly.
Two things stood out. One electrolytic capacitor near the power section had a domed top, the tell-tale bulge of a cap that's given up. And on the underside, a connector that takes mechanical stress every time something's plugged in had a hairline crack around one of its pins. A cold or cracked joint, the sort of fault that works intermittently for months and then doesn't.
the actual repair
The cracked joint was the easy half. Flux on the pad, fresh solder, enough heat to flow it properly and form a real fillet rather than the dull blob that was there before. The trick people skip is the heat: too timid and you get another cold joint, which is how you end up back here in a fortnight. You want the joint hot enough that the solder wets and pulls into a clean shiny cone, then off.
The capacitor was more work. Desoldering a through-hole electrolytic with a swollen body and old solder takes patience and a desoldering pump, or braid if you're being delicate. I noted the polarity twice, because fitting an electrolytic backwards is a mistake you make exactly once and then never forget. Out with the old, in with a like-for-like replacement of the same capacitance and voltage rating, a higher temperature spec because it was in the bin and good caps are cheap insurance.
Symptom: no power, no LED
Found: 1x bulged electrolytic (power rail), 1x cracked connector joint
Fix: reflow joint, replace cap (same uF/V, 105C rated)
Time: about an hour, most of it desoldering
Powered it on. The LED came up. I'd be lying if I said I didn't grin at it.
The thing I take from these jobs isn't the saved money, it's the reminder that hardware fails for legible, physical reasons. A capacitor dries out. A joint flexes until it cracks. There's no stack trace, but the evidence is sitting on the board in plain sight, and an hour with a loupe and an iron is often all it takes to read it.