My success rate has been pretty low repairing PCB. Better when I was the original designer, but not 100%.
Mostly I used the bone pile for experiments, driving those portions that did work.
I've played with soldering iron since Junior High, now have a couple Metcals and a hot-air rework gun.
Need a Soldapullt for thru-hole.
A key to figuring out what's bad, assuming no obvious scorch or crater, is DMM with diode-check scale. Ohms and diode drop, both polarities, so you can tell which semiconductors have failed. I have been able to identify those correctly.
Also check voltage rails, could be crowbarred through transistors.
I have a couple failed front-load washers I want to figure out. They report "failed tachometer" but actually don't spin the motor. I applied DC and the motor ran, so something in rectification or PWM.