Pioneer SA-710 Repair

[Mrcoolest123]

Hello everyone! This is my first time trying to repair an AMP after previously working on various other pioneer machines, but I have met a problem that does not want to disappear.
I’ve gotten this Pioneer SA-710 for cheap because the last owner had trashed the internal in a pretty bad way. All main power and secondary power transistors burned, as did some resistors auxiliary to them. I studied the schematic and replaced all the wrong pieces apparently, and did a full electrolytic capacitor replacement on the unit too for good measure. Before the unit had its transistors repaired, the protection relay functioned, but since no power transistors were in the machine, nothing happened. Now after the replacement, one of the relay channels has no voltage, that is expected from a unit that has nothing plugged, but the other one has -34 volts on it, and the replay magnet part that is supposed to receive the maximum 24 volts is receiving 34 volts. Initially, I had only changed the same pieces in both channels, so I started comparing voltages from the “working one” with the "defective one” and saw that the voltages on the non-working one were ALL out of spec, so I started replacing parts. I’ve reached a point now where I practically replaced all parts of one channel, but still haven't resolved my problem! Does anyone have any tips on where I should look now?. (Replaced parts in green)

 

[ConradH]

Shotgun parts replacement often leads to more problems than when you started. I'd go through the board with an ohmmeter on the diode setting and check all semiconductors. I'd also measure all resistors. I'd check capacitor polarity. I'd get a bright light and do a really close visual, looking for bad joints and cracked traces. Before power-up I'd remove the 3+1 bias diodes and short that string out. That will remove most of the bias voltage. The reason I'd do that is because those all-in-one diodes are fragile and you probably don't have any quick and easy way to test them. If they go open, things fry! After everything is working, you can address that issue. I'm not normally a fan of dim bulb testers but in this case you really need one.

 

[Mrcoolest123]

Shotgun parts replacement often leads to more problems than when you started. I'd go through the board with an ohmmeter on the diode setting and check all semiconductors. I'd also measure all resistors. I'd check capacitor polarity. I'd get a bright light and do a really close visual, looking for bad joints and cracked traces. Before power-up I'd remove the 3+1 bias diodes and short that string out. That will remove most of the bias voltage. The reason I'd do that is because those all-in-one diodes are fragile and you probably don't have any quick and easy way to test them. If they go open, things fry! After everything is working, you can address that issue. I'm not normally a fan of dim bulb testers but in this case you really need

Thanks! I’ll do all that. but could you specify a bit more about which ones are the so-called “3+1 bias diodes” and the "string I should short.” I already have a dim bulb tester that I use, and have to say, love using it! Saved me a lot