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Old 6th December 2005, 11:57 PM   #1
Brado is offline Brado  United Kingdom
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Unhappy Marantz PM75 will not power up?

Can anyone please help?
The power button indicator light comes on, but fails to power up the amp.
This has happened before. After switching off and on a couple of times, it was OK, but not now.
For some time, now the frequency LED's do not stabilize on one frequency, usually 48k, but alternate between 32k, 44k and 48k. This may have a bearing. Also, but not very often, a low hum is heard, but this will stop if I switch off and on again.
I usually can do most electronic repairs, but I need guidence with this one since I do not have any service sheets.
Thanks
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Old 14th December 2005, 05:46 PM   #2
lineup is offline lineup  Sweden
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Should be something about powering up circuit or protection.

I would measure round rectifier and big power supply caps.
Try to find out if some cap has bad connetion to board.
Maybe a some components in slow start/stand by circuit is not conneted alright.
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Old 14th December 2005, 08:12 PM   #3
Brado is offline Brado  United Kingdom
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Thanks.
After 4 days it's powered up again, but the frequency led's still flicker. I think you are right about the cold connections. when it next stops working, I will try resoldering all connections that you have suggested
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Old 14th December 2005, 08:12 PM   #4
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I agree with lineup.

It sounds like a posible dry joint on one of the main smoothing caps or supply to that rail. Humming is usually caused by this.
Also if other parts of the circuit take supply from this rail they will be affected.

Look under the main caps etc for some arcing or black burn marks from the possible bad connection.
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