A little dev board that had been perfectly happy on my bench for months simply stopped powering on. No light, no life, nothing on the serial console. The kind of fault that makes you assume the worst and start pricing up a replacement.
Before ordering anything I did the cheap diagnostics. Continuity beep across the power rail: fine. Voltage at the input: present. Voltage anywhere past the barrel jack: nothing. Which narrows it down nicely. I wiggled the connector and the rail flickered, the universal sign of a mechanical solder joint that's given up under the strain of being plugged and unplugged too many times.
Under a loupe the joint had a hairline crack right around the pin, the dull grey ring of a connection that's fatigued rather than failed outright. Five minutes' work: a dab of flux, reheat the joint, feed in a touch of fresh solder so it flows into a proper shiny fillet, let it cool without breathing on it. Plug it back in and the power light comes on like nothing was ever wrong.
There's a particular satisfaction to fixing hardware that software never quite gives you. The fault was physical, the fix was physical, and the result is sitting on my bench blinking happily instead of in a bin. Reflow the joint, not your patience.