tamas4president
New Member
Trying to repair Harman Kardon PM660. I am a novice however amp has sentimental value. And sounds/sounded super nice.
Apologies if my terminology is not right....
Main Symptom:
Left Channel is significantly weaker when passing through pre-amp.
Things to note:
- Everything sounds fine when using 'Main Direct' which bypasses the pr-eamp.
- The amplifier circuit, caps etc all seem fine as able to crank it up with 'Main Direct' on.
- Confirmed with Osiloscope and sine wave that output is clear when 'Main Direct' off.
- Checked the main direct switch in both on and off position. It has 12 poles with 4 sliding clips that short between the middle and one adjacent pole in 4 groups of 3, (2 either channel)
- did not measure voltage differences between the channels, would that help?
Questions:
- How can I go about fixing something likes this, do I simply trace things backwards?
- Is there known issues in these amps or pre-amp circuits in general that might have such a symptom.
Apologies if my terminology is not right....
Main Symptom:
Left Channel is significantly weaker when passing through pre-amp.
Things to note:
- Everything sounds fine when using 'Main Direct' which bypasses the pr-eamp.
- The amplifier circuit, caps etc all seem fine as able to crank it up with 'Main Direct' on.
- Confirmed with Osiloscope and sine wave that output is clear when 'Main Direct' off.
- Checked the main direct switch in both on and off position. It has 12 poles with 4 sliding clips that short between the middle and one adjacent pole in 4 groups of 3, (2 either channel)
- did not measure voltage differences between the channels, would that help?
Questions:
- How can I go about fixing something likes this, do I simply trace things backwards?
- Is there known issues in these amps or pre-amp circuits in general that might have such a symptom.
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