I have a Marantz PM-17SA. This model should be close to the PM-15S1. The sound from left channel is small and distorted after using for 7 years. Sometimes after run it for few hours, the sound becomes normal. I try to repair it by myself, but I don't have this kind of experience before. I get the service manual, and check the schematic of PM-17SA. I apply a 1KHz sine wave input with I-POD and measure the preamp output and main out with an oscilloscope. I do not hook up the speakers. The preamp output of both channels looks good. But at the main out, the waveforms between left and right has little difference. The left channel looks distorted at the rising crossover point, and some high frequency noise appears at maximum amplitude. Can anyone give me some suggestions for next step? Is this problem possible coming from the electrolytic capacitors on the power amp PCB? Replace these electrolytic capacitors might solve the problem? Thank you.
The distortion might be caused by a resistor. The loss of volume could be the capacitors, but you could try injecting signals into the transistors to see if any has gone. They can cause the distortion and loss of signal. If you apply a soldering iron to any part it will heat up quicker, or you could also use a hairdryer for the whole thing. You can also get a freeze spray that cools things that have heat sensitive faults (available from electronic parts shops).
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