Hi to all.
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.
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.
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Maybe your output DC is a little bit high and trigger the protection circuit.
You can check the output DC and power transistor bias current before the protection circuit ok or not.
You can check the output DC and power transistor bias current before the protection circuit ok or not.
Could be your Bias and/or Offset Variable Resistors have gone flaky and need changing? Ive had the same problem a few times now so I always change the Variable Resistors to sealed 25 turn types.
patrick101
Output Offset is 0.05 ~ 0.10 mV
I have check it and before the relay. I think it is OK.
redrooster
Do you suggest me to replace the variable resistors;
The service manual marked as "semi-variable resistor".
It is a problem? Can I use a trimmer?
Output Offset is 0.05 ~ 0.10 mV
I have check it and before the relay. I think it is OK.
redrooster
Do you suggest me to replace the variable resistors;
The service manual marked as "semi-variable resistor".
It is a problem? Can I use a trimmer?
Good point, old pots can be a bit crusty and may appreciate a bit of isopropyl alcohol at least (or suitable contact cleaner, like DeOxit D5 or similar). Swapping them out is not usually necessary in a well-designed circuit, unless they are literally falling apart (the Pihers in old Grundig amps are doing that at times).
My prime candidate would be the offset pot. Maybe do a sanity check of its operation with the multimeter.
EDIT:
Hmm. Please measure the voltage across each of the 0.22 ohm resistors. Anything more than 10-15 mV to be seen here?
If so, check resistor values to the best of your abilities (measuring sub-1 ohm resistors can be tricky on a basic multimeter, but compare a few to be sure).
If not, something in the protection or relay driver circuit may have chosen an unlucky time to pack it in.
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Hey, I´m new to the forum and have the same issue.
In the moment I moved the DC-Offset poti the protection went on and is now in this state permanently.
I checked all the resistors in the protection section off the board, on the basis of jimakos problem, but they all seem ok.
Any other ideas what the problem might be?
In the moment I moved the DC-Offset poti the protection went on and is now in this state permanently.
I checked all the resistors in the protection section off the board, on the basis of jimakos problem, but they all seem ok.
Any other ideas what the problem might be?