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No Sound from SX-780 Receiver

Hello!
I just tried connecting my SX-780 and cannot get any sound out of it. I've tried the radio, auxiliary input, etc., but to no avail. Does anyone have any ideas for me?
Thanks!
justjeffb



No Sound from SX-780 Receiver

Regulator transistor may be bad. It is mounted to a small heat sink, which is way too small, as these regulators run hot.
The protection IC can go bad (this is a Pioneer part). One of the audio output modules can be bad.
Less likely, dirty tape monitor switch.

No Sound from SX-780 Receiver

Johnnysan,
Thanks for your prompt response to my inquiry. How involved is repairing any one of the possible problems mentioned above? Is it worth repairing? Thanks for your help.
justjeffb

No Sound from SX-780 Receiver

Replacing the regulator is not hard; I like to mount them to the power amp heat sink, but this is more involved and the transistor must be insulated and wires run to the circuit board.
The first thing you need to do is find out if the protection relay is staying off; if it is always off then you have an audio amp problem (one or both of the power amp modules is probably bad). The easiest way to test a module is to remove all the solder from the pins of one module, then turn the receiver on; if the relay closes then that module is bad and is preventing the protection circuit from powering the relay. I don't know if those STK0050A modules are still available (I have a few but I'm not sure if they are good).
The PA3004 IC might be bad (protection IC); these may not be available either; it is a Pioneer part exclusively (IIRC).
If you had a bad audio module then you need to test the resistors near this part; they can be open. The STK0050A crosses to an NTE (or ECG) 1281; if you get lucky you might find some on eBay.
The 780 is a nice sounding receiver, but I prefer discreet components as they are still fairly easy to find; if you like the 780 it would be worth repairing.