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Marantz PM66 se problems, information wanted
Marantz PM66 se problems, information wanted
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Old 13th April 2007, 01:22 AM   #1
alan_w is offline alan_w  United Kingdom
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Default Marantz PM66 se problems, information wanted

I have been doing some research on this amp as my own has been having some problems, in that the right side output channel is at a lower volume than the left, which wasn't the case about 2 months ago.

Whenever I put in this amp into google it comes up with this website, and from what I have read I assume that this site is full of people who know far more than I ever will about this subject, so, like a moth to light it drew me in.

I am not totally sure what the problem actually is yet, I have ruled out the CD player (Marantz CD-48), the speakers (Kef Q35) and the cables (QED) and narrowed it down to the amp right hand speaker channel.

I have been told that Leaky electrolytic filter caps will result in audible hum, as there is no hum that rules that out. The thing is, the sound is good on both channels, but the left channel is quite a bit louder than the right, meaning that the balance has to be almost all the way to the right to actually balance it.

Does anyone have any ideas/hints/tips? Where can I get a schematic from so that I can start detailed diagnostics?

If it helps, I took some photos of the insides of the amp, mainly to document, but also incase it showed anything obvious up.

Thanks for your help, I appreciate it.
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Old 13th April 2007, 02:21 AM   #2
Leolabs is offline Leolabs  Malaysia
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Leaky signal/feedback caps or dirty volume/balance control.
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Old 13th April 2007, 10:41 AM   #3
alan_w is offline alan_w  United Kingdom
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Sorry, I forgot to include the link to the photos. Probably won't help but I include them anyway (tried to look for a way to edit the OP but couldn't find one).

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Old 6th May 2007, 06:59 PM   #4
Juko is offline Juko  Netherlands
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I had the same problem with a Yamaha amplifier. Cleaning the speaker protection relay-contacts solved the problem.
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Old 15th July 2012, 09:29 PM   #5
watson427 is offline watson427  Italy
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I have just experienced a similar problem (10% volume from right speaker vs 90% volume from left speaker) on my Marantz PM66 SE. Did your problem ever get resolved? If so, any pointers?
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Old 16th July 2012, 07:45 AM   #6
Mooly is offline Mooly  United Kingdom
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Marantz PM66 se problems, information wanted
Electronic faults causing gain problems are very rare, the causes are usually simpler.

First steps would be to use a scope and known signal source which would find the problem area in seconds but I'm guessing you haven't got one

So you need a test CD with a test tone of around 100 to 1Khz and a DVM that can read AC voltage reasonably well. It doesn't need be accurate so much as have good resolution at low levels. It should be able to resolve a voltage of say 1.22 volts and not just show 1 or 2 volts.

You would then check (no speakers connected) at the amp outputs first with the test tone playing and confirm that there is a difference between channels. Set the volume to give around 10 volts AC.

Assuming there was a difference then you next check the AC voltage at the input to the volume control to "split" the amp in half and determine where the problem is.

Most faults like this are caused by faulty controls such as balance, volume etc and by cracked (damaged) print.
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Old 16th July 2012, 08:13 AM   #7
pitbul is offline pitbul
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Check the input selector, if it is mechanical problem is there. Probably oxidation and contacts of gold are full of black film over it. Use contact spray to clean the input switch, or if you have knowledge disasemble switch and clean the contacts. 10 years is enough to make that film on gold contacts.
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Old 6th August 2012, 12:33 PM   #8
dungochop is offline dungochop
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Thumbs up Dry Joints Galore!!!

Just repaired a Marantz PM66-se audio amp with no speaker relay operation and discovered -38 volts on L751 output coil (Left Channel). Traced fault back to input of channel and found R719 68ohms O/C emitter resistor for Q701, to find Speaker relay intermittently working and sometimes clicking off... dry joints galore on main board was the cause,also the "source direct button cut out left channel....you guessed it, dry joints on Source relay board!!

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Old 6th August 2012, 06:13 PM   #9
madtecchy is offline madtecchy  England
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I was about to say lots of dry joints but was pipped to the post.
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Old 28th March 2015, 04:13 PM   #10
MJFear is offline MJFear
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Default PM66SE KI Sig also humming

Hi all,

I have a Marantz PM66SE KI Sig that also has hum on the R channel. Until recently it spent 10 years in its box in my attic and now want to use it again.

I took the top off just now and noticed that the two large blue Elna capacitors have leaked onto the circuit board. Can anyone tell me if this is likely to be the cause of the hum, and give me an idea if it is repairable please? I don't want to throw good money after bad getting it assessed by the Marantz repair shop if it is already junk.

Many thanks

Mark Fear
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