Broken Marantz PM 53 speaker amplifier

Hi all, I have an old Marantz amplifier that mostly works but keeps on clicking which cuts out all sound from the amp. The amp stays on but no sound comes out until it clicks again turning the sound back on. I have the necessary tools and skills, like soldering if needed, to fix it but no idea where to start as I am somewhat new to the hobby. It sounds like some sort of relay that might be faulty but I’m not sure. The amp powers a pair of Kef Q35 speakers.

What you describe sounds more like the power supply or start up delay being faulty.

I have looked inside my dads old PM72. Maybe the schematic of the PSU matches the one in the PM53.

Oh, I did find a schematic for the PM53 but I couldn’t figure out what I was looking for. Is there any way I could fix it myself?

There should be a relay (relatively big box on the PCB), look for dead capacitors it is connected to.

Edit: Some pictures of the insides would be helpful. Couldn’t find any of the PM 53 online.

I did a bit more searching apparently it is a common problem with older Marantz models. It is some sort of protection circuit that has capacitors that seem to fail. I can not really see any blown capacitors in mine though.

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Oh kay. This is going to be fun to trouble shoot.
One simple power on delay is with an NTC thermistor slowly charging a capacitor until the relay can trigger. Look for a round/oval thing on a board position that is not marked with a “C” or “R” (followed buy a number) similar to this (might be black with white letters):

Electrolytic caps don’t explode/blow, the electrolyte permeates through the plastic parts of the casing over time.

Looking at the photo, you probably want to pull that PCB out the corner. I have the suspicion the black ribbon cable controls the relay. Can’t say for sure without seeing the traces.

I looked for a similar component but could not find anything. I also noticed we have the old 01 model that has a manual switch for the input voltage and my dad originally set it on 220V but South Africa has a voltage of 220 to 230. So I am not sure if I should set it to 240V to see if that was the cause of the problem.

I found a PDF of the original service manual that has a whole diagram if that helps.

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The service manual is a very nice find.
So the block diagram of the relay control is this here:

In circuit, it is this:

Following the traces, it is either the decoupling capacitor in the pink box, or something on the PU01 sub-assembly.

Looking at PU01, I realy hope it is the decoupling cap.

So this mute relay is not controlled by an NTC thermistor, but by a pair of transistors controlled by a micro controller. :neutral_face:
I realy realy hope it is just that capacitor gone bad.

So? It was that capacitor? I have the same on-off behaviour with no apparent reason.

I was quite busy the last 2 months so I was not able to do the repairs but after I cleaned it and reassembled it, it is working fine. It still does it but way less often. So I am not entirely sure what is happening.

I opened mine and resoldered the final stage and the driver transistors. It’s working properly now. It must’ve been a loose pin on one of them.

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The joys of lead-free landfil material electronics.