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Old 28th August 2016, 11:10 AM   #1
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Default Marantz PM82 fault

Hi everyone. I have a lovely old PM82 that has suddenly stopped working so I'm trying to make an initial diagnosis to try to figure out what bits and pieces I might need to source before I tackle it. While I have a good technical base I don't have a particular skill for electronics, but I have patience and a determination to solve this problem. The PM82 was working perfectly with no indications of a developing problem until it suddenly stopped all output (both speakers 1, 2 and headphones). All other aspects of the amp (power on, source selector, etc) seem to work fine. I assumed it was probably something simple like a fuse in one of the power supply boards, but they're all fine. Definitely no problem there. Has anyone got any experience of this kind of problem and some advice to help determine the exact problem. Thanks in advance. Marantz PM-82 - Manual - Stereo Integrated Amplifier - HiFi Engine

Last edited by Coles; 28th August 2016 at 11:28 AM.
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Old 28th August 2016, 11:23 AM   #2
Mooly is offline Mooly  United Kingdom
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I'm not familiar with this specific amp but there are a couple of basic checks.

1/ Check that there is no DC offset at the output of each power amp. This must be measured before any speaker relays. 99% chance one channel has a large offset typically meaning that the output stage has suffered a failure.

2/ Fault finding always includes checking all relevant internal supplies by measurement and make sure those supplies are reaching their destination.

Odds on this is going to be blown outputs and drivers. Cause ? could be anything from a dry somewhere through to a transistor (typically the VAS or voltage amplifier stage) breaking down intermittently.
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Old 28th August 2016, 11:38 AM   #3
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@Mooly, Thanks for your reply. That gives me a bit of direction. I'll do a bit of study and post up my experience in tackling it. Any and all other thoughts welcome.
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Old 28th August 2016, 11:49 AM   #4
Mooly is offline Mooly  United Kingdom
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Just measure the offset for starters. You should have essentially zero volts (less than -/+0.05 volts) on R767 and R768. Those should be easy to identify and measure on.
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Old 28th August 2016, 03:55 PM   #5
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That's great help! I'll post up some images so others might benefit from this thread in the future. Click the image to open in full size.
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Old 28th August 2016, 08:36 PM   #6
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To save you time, do the loudspeaker relays engage? If they do, there is no problem with DC on the output stage, it may be more in board.
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Old 28th August 2016, 09:55 PM   #7
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Jon, thanks for your interest. I won't get a chance until later in the week to take the lid off the amp again but I was working on the assumption that the headphone outlet should work regardless of a problem with the speaker relays? Also if there was an issue with a relay (LN01 or LN02) then the other set of speakers should work regardless? I could be just plain wrong on these assumptions and I appreciate your input on this issue.
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Old 3rd September 2016, 12:30 PM   #8
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Protection deactivates the total circuit for both relays if exist ...To save some time if relays simply click that is most of the times enough to tell you that the amp section is OK search for the problem elsewhere .

A few pointers
There is P851 power supply board check fuses , flip over to check soldering issues around the regulators...then check all voltage present in the output of each regulator .

There is plenty of fuse resistors around the amp 4.7 -100 R you need to check these also

As a rule of thump these amplifiers suffer from soldering issues driver area and Vbe multiplier the most

Focus in 24V rail since this feeds the relays and the protection circuit

replace all capacitors around the protection area IC QN01 check other small capacitors for leak or failure

After done adjust bias according to the schematic and make sure that you read it correctly...

Kind regards
Sakis
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Old 5th September 2016, 08:14 PM   #9
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@Sakis, That's a real help. Thanks. I'll post some updates when I get a chance to examine the circuits.
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