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Old 4th January 2008, 01:15 PM   #1
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Default Problem with Marantz PM-66SE amplifier

Hi everyone

My Marantz PM-66SE KI Signature amp just came out of storage yesterday and seemed to be working fine. This morning, however, it's suddenly developed a fault - must be the shock of being used again!

The problem seems to be with the right input channel. The sound is only coming out of the left speaker but both speaker outputs are working. The problem also occurs whatever input device I use - cd player, record deck. So I can only assume the fault is somewhere in the processing of the right input channel in the amp.

Does anyone have any idea on where the fault might lie on the circuit board. I'm not familiar at all with the inner workings of hi-fi equipment but I'm willing to have a go at fixing it, so any advice would be much appreciated.

Thanks very much

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Old 4th January 2008, 06:25 PM   #2
Chudley is offline Chudley  United Kingdom
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Join Date: Mar 2007
The service manual for the pm66se is below - it's the same circuit design as KI so might be helpful in finding the problem if you are confident enough to look yourself.

If you switch on source direct and it makes no difference, and you have checked your speakers by swapping them between channels then the problem must lie at some point in the amp on or after the ribbon cable from the input pcb. When you say the output is still working but there is no sound - how do you know the output is still working?

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Old 4th January 2008, 06:25 PM   #3
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Hi folks

Just a quick update as I think I got a bit confused swapping stuff around. There's actually nothing coming out of the amp's right output channel - sound is only in speaker connected to left channel. Don't know whether this simplifies the problem but let me know if you have any ideas.

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Old 5th January 2008, 01:45 PM   #4
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Thanks Chudley, I got the service manual ok.

I've had a look at the circuit diagrams and tested quite a few of the resistors on the main board including the R802 and R807 that have been mentioned elsewhere. These all give correct values apart from R769 and R770 which show virtually no resistance at all, but they are both in parallel with coils. Would the meter be measuring the resistance of the coils in these cases?

The other possibility I was looking in to were the relays, LN51 and LN01. The fact that these are mechanical and have moving parts might make them more susceptible to breaking if they have not been used for quite a while. However, I'm a bit unsure as to how to test if they are working - presumably I'd need to prove that, when triggered, the output voltage is the same as the input for each switch in the relay. How would I do this in practice though? Getting under the circuit board to access the inputs and outputs of the relays and poking around with the meter whilst the amp is switched on sounds a bit risky. If someone could advise me on this, I'd appreciate it.

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Old 5th January 2008, 07:29 PM   #5
Chudley is offline Chudley  United Kingdom
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R802/R807 supply QN04 (protection IC) so if these had gone the protection relay LN01 wouldn't click in at power up - you wouldnt get any audio output on either channel if anything was wrong there.

It is possible the relay could be at fault as you say - although I'm no expert (thats putting it mildly), I would probably recommend checking the resistance across the trimpot R755 (sets the idling current), along with resistors located around there as well. Compare R755 resistance against R756 on the working channel. The trimpots often go bad over time with dust etc.

When Q763, Q751, Q761 (power transistors & driver) blew in my PM66 the power fuse blew whenever it was switched on so I would not expect these transistors have gone open circuit but you could always check resistance between legs of each and compare to the good channel just to be sure. The solder joints for the speaker terminals have also given me problems in the past, causing one channel to drop out intermittently and finally permanently, so you could also check there.

If you aren't comfortable poking around inside the amp when switched on then dont! Not only could you give yourself a nasty jolt (especially from the mains terminals) but you could also short something out and cause more damage. Dont forget the large capacitors C801 & C802 will hold charge for a while after you power off and they could give you a nasty shock if you touch the terminals or short them out!

Good luck!
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