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Marantz PM6004 amplifier cutting out at low volume

David B

Dec 29, 2017
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Hi, I have a Marantz PM6004 audio amplifier that sometimes cuts out on one channel (can be either channel) when I switch source direct on or off at low volume. Also does the same if I switch between speakers A and B. If I turn the volume up the problem resolves itself. I have cleaned the volume pot and the A, B and Source Direct switches with Servisol contact cleaner. But the problem is exactly the same. Also I don't think it's the Bass, Treble or Balance controls as source direct bypasses those. The speakers are fine as they work perfectly with another amp. And I think the connections from the amp to the speakers are fine too. I read somewhere that the relay can cause this problem. The relay looks like a sealed unit (please see photo) so I'm not sure if it can be cleaned. There is a site selling a new relay ( HANDOUK BC3-12) , spares2repair at £16.99 but Im not sure if I want to buy one if its may not definitely be the cause of the problem. If the relay may be the cause but I can't get into it to clean the contacts properly could I simply drill a small hole in the relay case and squirt some contact cleaner in it? I have been running two pairs of 6 ohm speakers on the amp (the manual specifies minimum 8 ohm speakers if running 2 pairs) is it possible I have damaged the amp? I have never turned it up more than half volume.
 

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Ylli

Jun 19, 2018
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Sounds exactly like a relay problem. And that is actually quite common. Try this... when it is acting up at low volume, tap on the relay with the handle of a screwdriver and see if the audio comes back. If it does it is definitly the relay.
 

David B

Dec 29, 2017
43
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Sounds exactly like a relay problem. And that is actually quite common. Try this... when it is acting up at low volume, tap on the relay with the handle of a screwdriver and see if the audio comes back. If it does it is definitly the relay.
Thanks, I just tried tapping the relay but it didn't seem to make any difference (I didn't want to tap it too hard just in case I damaged something). I did find though that switching the amp off and on again would sometimes bring back the weaker channel. Could this suggest it could still be the relay? If so im not sure if I can get into the relay to clean it properly (looks like a sealed unit, unless I can peel of the plastic underneath (where the pins are?) failing that is it ok to drill a hole in the relay case and squirt some contact cleaner in there, to see if that helps before paying for a new relay?
Cheers
 

David B

Dec 29, 2017
43
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Thanks, I just tried tapping the relay but it didn't seem to make any difference (I didn't want to tap it too hard just in case I damaged something). I did find though that switching the amp off and on again would sometimes bring back the weaker channel. Could this suggest it could still be the relay? If so im not sure if I can get into the relay to clean it properly (looks like a sealed unit, unless I can peel of the plastic underneath (where the pins are?) failing that is it ok to drill a hole in the relay case and squirt some contact cleaner in there, to see if that helps before paying for a new relay?
Cheers
Hold on a minute, I have just been looking at a photo of inside, there seems to be relays everywhere!!!??? I was just looking at the relay near the volume control. It looks like there is a relay on the power supply board, 2 near the speaker terminals and another one just in front of those as well!!!??? Please see photo, which relays could be the most likely suspects or could it be all of them???
 

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David B

Dec 29, 2017
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S7501 for the left channel and S7502 for the right channel would be the likely culprits. They are Fujitsju FTR-F4AK012T. You could try, but I don't think you will have much luck cleaning them. One source would be https://www.mouser.com/ProductDetail/Fujitsu/FTR-F4AK012T?qs=N2nzcguIp804V2KGwS7fIA==.
View attachment 57502View attachment 57503
Thanks that's very useful. It also makes sense. Are these two relays for switching between A and B speaker channels??? Because It is when I switch speaker channels the problem often occurs. Also I'm wondering if running 2 pairs of 6 ohm speakers (instead of the recommended 8 ohm speakers) has caused excessive sparking in those relays resulting in poor connections?
Happy New Year.
 

Ylli

Jun 19, 2018
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Yes, they appear to be for switching between Speaker 'A' and 'B'. As long as you are not pushing things, I don't think the 6 ohm speakers would be the cause - speaker relay failure/intermittants are actually quite common.
 

David B

Dec 29, 2017
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I tried tapping those relays with a screwdriver handle and the sound did change sometimes improving/sometimes distorting, I think the relay just in front of the 2 speaker switching relays is suspect too. I did try drilling holes in the top of these relays and squirting contact cleaner in there but it didn't seem to help at all so it looks like I will have to replace those relays as you suggested. I might as well replace the relay near the volume control too (even though it doesn't appear to be acting up YET?). I am guessing the relay on the power supply board should be ok as it is using higher voltages and less likely to cause problems? It looks like I will have to remove the main amplifier board to replace those relays. Do I need to put on some kind of heatsink paste where the board screws onto the heatsink when I put the board back?
Cheers
 

Ylli

Jun 19, 2018
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I might as well replace the relay near the volume control too (even though it doesn't appear to be acting up YET?).
Not sure what relay you are referring to here. S7503 turns the headphones on and off.

I am guessing the relay on the power supply board should be ok as it is using higher voltages and less likely to cause problems?
Yes.

It looks like I will have to remove the main amplifier board to replace those relays. Do I need to put on some kind of heatsink paste where the board screws onto the heatsink when I put the board back?
Without the unit in front of me, that's hard to say, most likely not as the 'board' doesn't need to be heatsinked. If you take something apart where thermal paste is used, it is best to clean off the old and put in some new.
 

David B

Dec 29, 2017
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Ok thanks, I might just try replacing the 2 Fujitsju speaker switching relays as these are the most likely suspects and are also easier to obtain than the Handouk relays.
 

David B

Dec 29, 2017
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Not sure what relay you are referring to here. S7503 turns the headphones on and off.


Yes.


Without the unit in front of me, that's hard to say, most likely not as the 'board' doesn't need to be heatsinked. If you take something apart where thermal paste is used, it is best to clean off the old and put in some new.
I have just replaced the 2 Fujitsju speaker relays and the amplifier now works perfectly, good as new It wasn't the easiest job, I had to remove the main board. I also had trouble removing the relays, my soldering iron wasn't really powerful enough to melt the solder easily, but I managed in the end with an extra pair of hands wiggling the relays whilst I applied heat to the joints with my soldering iron. I know it's too late now but I was just wondering if sockets are available for these relays ??? So the next time they need replacing it would a simple 5 minute job ( remove cover, pull out old relays, push in new relays, put cover back, job done!).
Thanks for all your help and advice
 

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Ylli

Jun 19, 2018
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Glad it is working well for you. I would not recommend sockets as those can cause more problems than they solve. The new relays should last many years.
 

David B

Dec 29, 2017
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Glad it is working well for you. I would not recommend sockets as those can cause more problems than they solve. The new relays should last many years.
Thanks again, I recently read somewhere that it is a good idea to turn the volume fully down before switching an amp on (and off?) apparently doing this will prolong the life of relays. I guess doing this results in less sparking between the contacts.
 
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Bluejets

Oct 5, 2014
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Normally it's to stop or reduce the large "pop" through the speakers, nothing to do with relays.
 
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