Marantz PM66SE

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dymaxion

Member
Joined 2006
Talking about repairs...
If the headphone works fine... but the speaker outputs one of the channels is silent then what is likely to be broken?

I thought that the headphone socket + cutoff happened at the very last stage of the amp.

If the output stage for one of the channels was dead woudl there still be sound on the headphone? Perhaps the output protection has blown? Or a capacitor blown in that stage?

Sounds like it might be a trivial fix?

Unless the Marantz has a complete separate circuit for the headphone amplification?

Any schematics & pointers appreciated.

Thanks
Spencer
 
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toman_9

Member
Joined 2006
Hi guys!

Bad news... I have changed all the transistors on the amp.
First the left channel then the right...
After changing the left transistros and turning on, everything seemed to be all right. And I tried with the speaker and a test signal.. I could hear the music and saw that the AMP was working.. (only one channel thou...)

However, when I placed the right channel transistors, and turned the AMP on, immidiately the fuse has blown... :(
I measured one of the power transtors (q761) to be broken...

What can go wrong here ? I changed all the transistors to be sure... I measured some resistors and caps.. everything seems to be fine...:confused: :confused: :confused:

Now I got no idea... :bawling: :bawling:

Tim.
 
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toman_9

Member
Joined 2006
:) :) :) :) :) :) :) :) :) :)

This time good news guys!

I managed to repair the AMP it took me WHILE to do it... but at the end a happy end. Now it works!

The problem was really not easy to detect.
Power on... fuse blow... source a broken power transistor, shorting +38v to signal (0V)...

The question:
What can cause a power transistor to break ?
Answer :
An unexpected high-current ?
The question:
Where does this current come from?

And this was the turning-point of the whole effort. I started to search the root of this high-current that may cause to break the transistor. As I stated before all the components (inc. caps and resistors) around this transistor was OK... So what else could it be ?
It took me a while to figure this out...
My problem was: although I got one channnel working... everything broke again when the second channel was connected. Actually the answer was hidden in my posts. YES !!! I found it.. A shortcut between the channels can cause this kind of behaviour.
And ideed there was a short between the 2 channels both signal lines were really shorted... The faulty element was the RELAY, it somehow shorted both signals....
Silly me... I have changed the relay once a while ago, suspected that it was broken... changing it back to the original relay solved the problem. :) (Not to mention that along with the broken transistors)

Thanks to all who have supported me ;) I really needed so push sometimes.

NOW !!!! The second stage... Improvements : SE to KI...
I think I shall make another topic for that...
 
anatech

anatech

Administrator
Joined 2004
Paid Member
Hi Tim,
Congratulations are in order! I am very happy you stuck with it.

In the shop, we call that fault "struck by technician". These type of faults can easily brand the unit as not repairable. It's usually something simple.

Enjoy the unit for a little bit before divimg in again. ;)

-Chris
 
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Edison

Member
Joined 2005
I'm trying to diagnose a problem with a Marantz PM66SE KI.

The right channel output has significantly less gain than the left with inputs above 500mV. Also the right channel can not be driven in to distortion. At 3V rms input Lch is at 25V and 0.7% THD+N, Rch 12V and 0.03% THD??? Looks like I've lost some gain somewhere.

Can anyone provide me with the schematics for this unit so I can try and find the problem.

email edwardjcbell@msn.com

Thanks in advance

Ed
 
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Arian1966

Member
Joined 2006
PM66SE

Hi Everyone
This is my first posting, so please excuse the thick questioning. I have a PM66SE. When the power switch is pressed in, the red LED light comes on but I cant hear the relay turn on. The fuse inside is still in tacked. Can anyone give some advise to how to fix or repair...or is it a case I need to throw away and start again.

Also I would really appreciate a schematic diagram of the circuit inside.

Many thanks :)

Rich
 
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eborgard

Member
Joined 2004
This is a very common sympton. Get the PM6010 service manual at the following address: http://www.eserviceinfo.com/download.php?fileid=15368
THe schematics and layout are identical to that of the PM66SE although some transistor values have changed (no impact).

1) Check the transistor driving the relay as it is a very common failure in this amp
2) Check as well the output level at output stage (or relay input) to check there is no DC offset (if so, change all transistors in the faulty output stage).
 
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eborgard

Member
Joined 2004
Well, indeed the IC input stage performs better than many discrete designs out there... I personnally don't like the triple darlington output stage.
Anyway, as I wrote in a previous post, the amp is cheap and you get what you paid for. Don't spend time trying to improve this amp, there is little to do.... It will NEVER sound high end.
Personnally I kept the chassis, transformer, remote control stuff ... and replaced the main board with a hybrid tube, TDA7293 and bipolar design... which makes a very nice spare amp when I modify my main one.
 
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