Just bought a PowerBook G4 Titanium while on holiday, demonstrating my absolute lack of self control when it comes to cheap, lonely old Macs. Luckily it has the exact opposite broken and roughed-up bits of my other TiBook so I should be able to meld them into one quite nice one and one utterly awful one.
Sometimes a diode will simply decide that it is time for current to flow in neither direction any more.
This is possibly one of the most bizarre component failures I have ever seen. The rectifier in this PSU failed and had created a dead short. It turns out that two of the diodes had split in half while the other two had simply turned into 0 Ohm resistors.
The SE/30 Reloaded is alive! After months of chasing my own tail, so sure that there couldn't be a single bad solder joint or faulty component left to test, I finally had the brainwave of removing the CPU and putting it back in again. Sure enough...