Hi!
A good mate of mine has a MOSFET power amp he is currently repairing.
He has re-capped the amplifier modules and is trying to set the biasing (should be measured as 100mv across a biasing resistor when cold and 300Mv when warm according to the MFR)
Once he has set the bias correctly, it remains stable for a short time and then begins to fluctuate wildly - it seems to drift way off as soon as things start to warm up and then the extra biasing starts to warm things up further etc....
I have suggested that he try checking or replacing the zenners and small signal diodes and transistors, but is there anything else that anyone here has seen as a common cause of this kind of behaviour? Again, all of the electrolytic caps have been replaced, but there are a number of tantalum/poly caps too....
The rails remain stable and the power supply is a large transformer not a SMPS.
The amp in question is an ashly ftx2001 SERIES 3 .... i can get hold of the schematic if you are able to assist or suggest something else to check.
Thanks for any suggestions or advice!
CHEERS!
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