The only practical repairs are fixing bad connections or replacing bad fuses, electrolytic capacitors, transistors, and diodes. If a new fuse pops, suspect the high voltage inverter transistors, and you can often substitute a pair (they almost always blow in pairs) from an old supply, even a 200W AT model. But before substituting a different component, first verify the original's parameters - type. Transistor types include NPN and PNP if bipolar, MOSFET are N-channel or P-channel and also either logic level or standard level, diodes are usually regular or Schottky, and you also have to worry about maximum voltage, power, and amp ratings.