Is the fuse on the power supply blowing? Are you getting a good 12VDC?
I'd ohm out Q103 and Q104. Q103 is the "bottlecap" in the middle of the heat sink. These power supplies usually have the transistors' base/emitter/collector labeled (B, E, and C) on the bottom side of the board. With your meter set on low ohms (if not auto-ranging).....your meter should damn near zero out, or at the very least, show very low ohms. This applies to all of these measurments.
Check the "C" of Q103 to a leg of L101. Now check it to connector J3---pins 4 and 8.
Check "B" of Q103 to "E" of Q104 (Q104 is the TIP31). Now check it to R111, R112, and the positive leg of C108.
Check the "E" of Q103 to a side of ferrite bead FE2
Now let's ohm out Q104 (TIP31).....Check "C" to "E" of Q105. Now check it to R104.
Check "B" of Q104 to "C" of Q105. Now check it to R112.
It's not necessary to check the emitter of Q104. Electronically speaking, it was already check when you ohmed out the base of Q103.
This is all the main regulating componets in the 5V line except for U2 (LM305).
Edward