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Old 31st July 2014, 02:28 PM   #11
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running this without a load is the way to go. even offset near the rail voltage should not harm
you mean remove the mosfets?
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Old 31st July 2014, 02:36 PM   #12
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he meant nothing attached to amp's output
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Old 31st July 2014, 02:36 PM   #13
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I have replaced all Q2, Q3 and Q4. They are new. The only different is thatthay are BC550.
took care of pinout difference ?
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Old 31st July 2014, 02:37 PM   #14
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Originally Posted by pmchoong View Post
you mean remove the mosfets?
no, they are integrated part of the circuit. Load would be a Speaker. start measuring the voltages across the resistors like R7, R8, Z1, Q3 E-C, Q4 E-C.

then compare to the working channel. maybe only the value of R7 Needs to be changed a little bit or the value of Z1 is slightly out of spec.

does the offset run to - or + supply?

having too less voltage across R7 means positive offset and the way round
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Old 31st July 2014, 02:38 PM   #15
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Re-solder the 2sj 109 and its related components . Clean well the space between the legs of sj109 .
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Old 31st July 2014, 02:47 PM   #16
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Originally Posted by uli View Post
no, they are integrated part of the circuit. Load would be a Speaker. start measuring the voltages across the resistors like R7, R8, Z1, Q3 E-C, Q4 E-C.

then compare to the working channel. maybe only the value of R7 Needs to be changed a little bit or the value of Z1 is slightly out of spec.

does the offset run to - or + supply?

having too less voltage across R7 means positive offset and the way round
Voltage across R7 is 5.10V in the 2 seconds that I measured it.
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Old 31st July 2014, 02:49 PM   #17
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let the amplifier warm up! it makes no sense to Switch off after 2 seconds. again, does the Offset drift towards - or +?
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Old 31st July 2014, 03:04 PM   #18
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let the amplifier warm up! it makes no sense to Switch off after 2 seconds. again, does the Offset drift towards - or +?
It drifts towards the +.

If i let the offset to climb, it will trigger the speaker protection board.
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Old 31st July 2014, 03:09 PM   #19
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put away the speaker protection when bugtracking :-)
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Old 31st July 2014, 03:12 PM   #20
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put away the speaker protection when bugtracking :-)
wouldn't it burn the mosfets?
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