So it sounds like you're serious about repairing this yourself. Also sounds like you're going to repair it by the old "let replace parts" program, in which case you'd better plan on replacing every component on that power board, plus the two output transistors.
Otherwise, a little bit of test gear would be useful. First, make you a Dim Bulb Tester. Very simple in concept, some folks make very complicated versions but really all you need is a light socket in series with a receptacle of some sort. This way when you fire an unknown amp up, you have a visual indication whether or not the amp is shorted out. If the amp does have a major problem, the DBT limits current automatically (through the light bulb) so you won't burn up anything more in the amp. I'd make this DBT, unhook the transformer's secondaries, and fire the amp up on the DBT to make sure the transformer is good. No use going any further if the transformer is bad, not cost-effective to find a replacement.
A transistor checker like this Peak DCA55 is a very good little investment. It not only checks the transistors, it measures hfe, and furthermore, it tells you which pin is B C and E. Very useful. Sure you can use a DMM diode check to test a transistor, with a whole bunch of measurements...lots easier to use a little meter.
