Hi,
Only just joined and apart from my introduction this is my first post.
Hoping someone can help me out here.
My beloved Marantz PM7200 has developed a problem, occasionally when turning on I will get no sound from one or both of the channels, the only way to fix it is to turn the volume up to max and wiggle it about a bit and then the sound comes crashing in. It's usually fine after that.
It's a random fault and I can go weeks without it happening and then it will happen regularly before behaving itself again.
I've had it from new (so at least 20 years old), any pointers would be helpful, I don't think it's the protection circuit problem but I'm happy to be corrected (I've used some contact cleaner on all the switchs, dials etc. but doesn't seem to have improved things)
Thanks,
Only just joined and apart from my introduction this is my first post.
Hoping someone can help me out here.
My beloved Marantz PM7200 has developed a problem, occasionally when turning on I will get no sound from one or both of the channels, the only way to fix it is to turn the volume up to max and wiggle it about a bit and then the sound comes crashing in. It's usually fine after that.
It's a random fault and I can go weeks without it happening and then it will happen regularly before behaving itself again.
I've had it from new (so at least 20 years old), any pointers would be helpful, I don't think it's the protection circuit problem but I'm happy to be corrected (I've used some contact cleaner on all the switchs, dials etc. but doesn't seem to have improved things)
Thanks,
Welcome to diyAudio 🙂
Two things come to mind here. No sound that appears as you turn the volume up can be a symptom of tarnished speaker relay contacts. Its a common problem across many makes and models. A an insulating layer build up on the contacts and as you turn the volume up (so more voltage present at the output) it breaks through this layer and then works OK till the next time. If the relay can be opened then they can be cleaned.
That said it is unusual to have both channels faulty together but it could happen.
Perhaps as or even more likely is a poor solder joint some where, possibly even around the relay or around the input sockets or volume control. Only a careful visual inspection would locate that unless you could perform tests in the faulty state such as looking with an oscilloscope where the signal disappears.
Faulty joints look like this where you can see a ring of cracked solder:
Two things come to mind here. No sound that appears as you turn the volume up can be a symptom of tarnished speaker relay contacts. Its a common problem across many makes and models. A an insulating layer build up on the contacts and as you turn the volume up (so more voltage present at the output) it breaks through this layer and then works OK till the next time. If the relay can be opened then they can be cleaned.
That said it is unusual to have both channels faulty together but it could happen.
Perhaps as or even more likely is a poor solder joint some where, possibly even around the relay or around the input sockets or volume control. Only a careful visual inspection would locate that unless you could perform tests in the faulty state such as looking with an oscilloscope where the signal disappears.
Faulty joints look like this where you can see a ring of cracked solder:
Thanks for the very helpful reply Mooly, the things you mention make sense..
I will get the cover off and have a close inspection over the weekend.
A refreshing change to get some useful advice on an internet forum instead of the usual unhelpful "advice" i.e. That's a crap Amp, you should buy xyz, etc.
Cheers
I will get the cover off and have a close inspection over the weekend.
A refreshing change to get some useful advice on an internet forum instead of the usual unhelpful "advice" i.e. That's a crap Amp, you should buy xyz, etc.
Cheers
Thanks. Give it all a good visual inspection first. A few gentle taps and prodding with an insulated stick (pen or something) can sometimes reveal poor joints. Normally poor joints are on components and parts that are perhaps not machine fitted to the board such as sockets, controls, transistors on heatsinks and that kind of thing. Look them all over.
Good luck 🙂
Good luck 🙂