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Sansui R-50 Receiver - Cause of Failure?

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Arken

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Hello, I recently got into a Sansui R-50 Receiver, and the left channel was dead. In there I found 2 shorted transistors together with an open ceramic resistor and a literally burnt carbon resistor.

I'd like to know what caused what to fail. Did the ceramic resistor fail and thus cause a short in the transistors? Or is it the other way around?
Also, should I check for failure in other parts so that it doesn't happen again after fixing it?
 

audioguru

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Maybe the speaker wires got shorted? Then the output current would be so high that it causes the damage.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I'd like to know what caused what to fail. Did the ceramic resistor fail and thus cause a short in the transistors? Or is it the other way around?
The other way round.

Also, should I check for failure in other parts so that it doesn't happen again after fixing it?
It's essential that you replace ALL faulty components, and passive checks may well not be enough, otherwise it's just going to blow again.

Generally, as a professional service engineer, I would replace all semiconductors in the DC chain, plus any faulty resistors, and any suspect capacitors. It's not usually caused by duff capacitors though.
 

KeepItSimpleStupid

Well-Known Member
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There are usualy some < 400 ohm resistors nearby that may have changed value. The DC BIAS, the voltage across the sandstone resistoors. is usually set with no speaker or load attached. There is usually an adustment for this. You can use the other channel for a value.

Zero is a bad number, but usually no harm will come to the amp. It should not run away when the amp idles for an hour.

Also check the DC voltage at the speaker relay/speaker and make sure its not in protect. <|0.75| V is usually OK. The closer to zero the better.

Those sandstone resistors are known as wire wound fusible resistors.
 
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