Quote from: markorock37 on December 27, 2011, 06:45:21 PM
A bit more testing I found about 10V at pins 11 and 14 from driver transformer to Q2. Pins 12 and 13 from driver transformer to Q1 is less than a volt. Sounds like the driver transformer is bad to me. Its a model 28-4300
10V is a little low. Pins 11 and 14 should be at half the supply voltage (+47). They should go to that voltage when Q1 and Q2 are removed and should be about the same when a good pair of transistors are installed. You can see that R128, R137, R136 and R139 form a voltage divider. Some current goes through R132 but not much. C1 could be bad, but it wouldn't affect the voltage when no speaker is connected.
These transformers develop shorts between windings. Disconnect 11, 12, 13 and 14 and then check that those wires measure infinite ohms to 15 and 16 and to ground. Mercury Magnetic$ makes the only replacement transformer available. If you find a short, there are two more windings on the transformer that were not used in this amp. They probably just cut the wires off. Any chance you can see them and maybe solder a wire to them? One pair is Red/Orange, the other is Yellow/Green.
Do you know how to check transistors out of circuit with an ohm meter? Basically you should see a diode between base and collector and another diode between base and emitter. Collector to emitter should show a high resistance or open.