MarkC said:
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.
