SMPS's can be a son of a bitch to deal with. A few hints.....
The FET or transistor needs a + kick to the B or G to start
things. After that the feedback ( via isolators or a winding ) hold
things down.
FETS or Xistors will almost always fail DEAD short.
Current through a low ohm E or S resistor on the output is
measured. Too much current causes shut down (SD).
Shut-down is either totally dead, lowering freq, or changing pulse
width. You can often hear it ticking or screaming.
Shorts on the secondaries such as shorted Hoz out cause SD.
Secondary rectifiers NEED to be exact replacements or else...
If you dont see any obvious problem start with the electrolytics
in the primary side. Then over to the secondary.
BTW dont forget you are dealing with two grounds. One is
the HOT primary. The other is the cold secondaries.
enuf fer now
73 Zeno
LFOD !