![]() ![]() I tried disconnecting the wire which carries the audio to the main PCB from the ribbon cable plug, to make sure there was nothing nasty coming from the main PCB, but it's still there. As soon as you do this, a 3MHz sinewave is superimposed on the 100Hz signal from the generator. The low cut filter behaves fine until you engage it with the low-cut switch, at which point its output is connected to the ribbon cable leading to the main PCB. I replaced it and subsequently discovered this problem. After tracing things through using a signal generator and oscilloscope, I found U101 (4560) to be toast - with DC on all its inputs and outputs. The fault reported was that Channel A had no output with the amp configured in this way. The customer said that it gets used on bass duty, with the internal crossover and low cut filter activated on both channels, with the high output from the crossover feeding the hi-mid amp. ![]()
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