Apple /// Power Supply

In which case you need practice in repairing them ;-) More seriously, there are easy faults with SMPSUs and difficult faults. Easy faults include things like the mains filter cap[acitors going short-circuit nad blowing the fuse. Change the capacitors and it'll be fine. Difficult faults include the all-too-common short-circuit chopper transistor. It may have been damaged by some other component failing (say an open-circuit in the snubber network across the chopper transformer primary), and unless you find and correct that other fualt, your new chopper will fail at switch-on. And the shorted chopper might have damaged other components too (like burning out th ecurrent sense resistor im its emitter circuit, then taking out a couple of small-signal transistors too). In the case of this Apple /// supply, I have no idea where this capacitor is in the circuit (I've not seen the supply, I've not seen a shematic), but it doesn't sound like a difficult fault. Sometimes that's just what yuo have to do. Unless you have a source of schematics of obscure PSU boards... -tony