One of my little SBCs died. Not gracefully, not with a log entry I could investigate, just dead. No power LED, no boot, nothing on the serial console. The kind of dead where you check the power supply three times because surely it can't be the board itself.
It was the board itself. Probing around with a multimeter, the input rail had voltage right up to the barrel jack and then nothing past it. The jack moved very slightly when I pushed on it, which is the universal tell for a cracked solder joint. These connectors take mechanical strain every time you plug something in, and over a few years the joint fatigues, cracks, and quietly stops conducting.
the actual fix
The repair was almost insultingly simple, which is the best kind.
1. Flux the existing joints on the barrel jack pins
2. Reflow each pin: iron on, fresh solder in, two seconds, off
3. Add a little extra solder for mechanical strength
4. Check continuity from jack to the input rail
5. Smug satisfaction
The trick with old joints is flux. The original solder has oxidised, and trying to melt it dry just gives you a grey, lumpy mess that doesn't wet properly. A dab of flux and the solder flows like it should, the joint goes shiny, and you can actually see it form a proper fillet around the pin. If your reflowed joint looks dull and crusty, it isn't fixed, it is just sitting there pretending.
Continuity came back, I plugged it in with a certain amount of held breath, and the power LED lit. It booted, found its filesystem, and carried on as though nothing had happened. Total cost: about thirty pence of solder and half an hour.
I know a new board is fifteen quid and my time is worth more than that. But there is something genuinely good about fixing a thing that broke, rather than feeding it to landfill and ordering a replacement. A cracked joint is not a dead board, it is a board waiting for someone to be bothered. This week I was bothered.