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Old 12th September 2015, 01:44 PM   #1
zdr is offline zdr  Belgium
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Default Trying to fix an old Marantz PM-35MKII

Outputs were completely dead when I got it, but headphones were playing just fine. Checked the schematics and noticed that there is speaker protection relay in the output stage, but there was no clicking sound on power on/off Indeed, the relay coil was burnt. An aluminum foil around the 1A fuse might had something to do with it

Replaced the relay and the shortened fuse, and now on to a new problem: protection circuit excites the relay as soon as volume is turned just a little bit above dead silence. At the same time, trafo starts singing the music that is supposed to come out of the speakers, at higher volumes

Did not start the measurement yet, but wanted to share findings so far in case it's a known issue with this amp.
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Old 12th September 2015, 02:45 PM   #2
Mooly is offline Mooly  United Kingdom
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Sounds like a short on the speaker output somewhere, the protection tripping due to overcurrent. Just measure the resistance across the speaker terminals for a start.

As the unit seems to have been 'got at' I would look closely to make sure no other unauthorised mods have taken place
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Old 12th September 2015, 03:54 PM   #3
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Check output transistors. Probably all blown. Same for driver transistors and emitter resistors.
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