Customer's unit came in dead. I replaced 2 shorted output transistors Q506 + Q507 & 2 blown fuses and it powered up but is in the protect mode. I tightened the CD ground screw. I'm suspecting that one of the pre-amp ICs is bad. Before I order one what else could it be? Thanks for any suggestions. Mark
You need to check other related parts - small resistors, the emitter resistor, etc. You may or may not have a drive IC bad. A bad drive IC does not usually destroy the outputs, though it is possible on this model.
If you have a variac, you may be able to use a double-ended (POLARIZED) AC cord to bring up your voltages and look for offsets, excess bias, etc. This is easiest if there are TWO switched AC outlets. Loop the receivers power plug into one switched outlet, and use a double-ended cord to connect the other switched outlet to your variac. Bring up the variac as you normally would, looking for offsets or excess current draw. Don't do this (or be VERY CAREFUL) if the power cord plug has been shaved to fit older outlets - if the polarity is opposite between the two plugs, then you would have a dead short on the AC line. For this reason, you should only attempt this if you are an experienced repair person.
Mark Z.
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