identifying cause of burnt out resistors

Thread Starter

pjcfraley

Joined Sep 13, 2018
3
I am working to repair a Pioneer SX950 receiver. The left amplifier channel is not working and frys the voice coil of speaker woofer. I discovered two burnt resistors on the amplifier board (R37, R41, pictured). The transistor right next to one of the resistors had burn marks on it, but i think it was just residual from the resistor. Now need to identify the cause. The circuit protection is not working, but also thinking there may be an issue with the power supply board. Attached is schematic with problem resistors and transistor marked. If anyone could give me an idea of where to look that would be great
 

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abrsvc

Joined Jun 16, 2018
41
Do you have a schematic of the amp ?

Regards, Dana.
have you checked the output transistors yet? I suspect that one or more are shorted which is what started this mess.
I will look further in the service manual, but I would first check the outputs. The transistor that is circled appears to be part of the driver pair for the outputs. Since one channel is working, the easiest at this point is to A/B the 2 circuits. I would suspect a few more low value resistors are open as well.
Dan
 

abrsvc

Joined Jun 16, 2018
41
Ok is there a circuit diagram on it, if so can you take a picture with your mobile/camera and post.it..
Member of the old school, still have a flip-phone...

I do have access to a copier though. PM me an address and I'll send out a copy of the schematic.
 
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