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Sansui AU-X501, protection problem

Jimakos

Jimakos

New Member
Hi to all. Sorry for my English. It's not my native language.
After a repair in my Sansui AU-X501, I try to adjust the Bias and DC 0V.
During this adjustment the protection activated and form then is always on.
I check everything in the protection circuit and I can't find the problem.
The amplifier works fine. I bridge the protection relay contacts and sound is clear and loud.
Please help!!! I have this amplifier from new, for more than 30 years. I like his sound and I want to repair it.
 
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Welcome to AK.
Maybe you set the Bias too high? Not related to bias, did you check the DC offset at the speaker terminals for dc voltage.
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make sure the batteries in the meter are good.
 
Binkman, thank you for response.
I have thought that, because the time of activation of protection. Just the time of adjusting.
I adjust the Bias 3 times. Also NO DC Volts, on speakers I check 3 times that also.
 
If the protection relay is open (in protection) there will be nothign at teh speaker terminals. The offset needs to be measured at the amplifier, not at the speaker terminals.
 
So you could have problems with your actual protect circuit.

Do you have a service manual/schematic that gives you voltages to look for in the protect circuit itself? If so, I would start by checking those. It could be that the actual relay transistor (responsible for holding the relay contacts closed) is faulty.
 
slimecity said:
So you could have problems with your actual protect circuit.

Do you have a service manual/schematic that gives you voltages to look for in the protect circuit itself? If so, I would start by checking those. It could be that the actual relay transistor (responsible for holding the relay contacts closed) is faulty.
Click to expand...

slimecity
Here is the service manual. No voltages in protection circuit.
 
I did not look closely at the ser. manual for IC listed above? there is no description of the protect circuit so you have to trace back from the relay. is there power at the relay? no? then protect is on or faulty Does the relay coil test good? Yes? then you have trace the circuit back... I also did not see any projects regarding your amp. on AK search/ protection.

It may be as simple as 'aged or cold solder joints'. bad caps or faulty transistors in the protect circuit Any thermistors in the unit?
 
Last edited:
Please let us know which resistor in the Protection circuit was open - It may help others in the future etc - tks
 
The problem was the R20 (see PDF).
It is very hard to find because the service manual of my model not appears that resistor.
I found the service manual of AU-X517 that have the same PCB and the correct diagram.
So the troubleshooting was easy.:)
 

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