[mohawk1975]

Help ! I own a PM7200 for a good number of years now - recently it started to behave really strange - basically when it gets really hot it suddenly just jump into standby or shut itself completely off.

For years getting hot is quite normal for this amp, however it never switched itself off like this.

After shutting itself off if I turn it back on to continue playing music it seems to continue to play fine but from this moment on if I touch the amp with my hand on any part of the chasis it powers off again and it will keep doing this unless i shut it down and leave it to cool for an hour or so and then it seems to behave normal again.

I know this isn't a particularly new amp and I have seen articles about heating issues with this amp but was wondering if someone had any views about my issue and any idea what I can do (if anything).

[surayne]

I've got the same amp, and it does run pretty warm, particularly in Class A mode. Switching off at a touch sounds like a short circuit or leak to the chassis though - I'd get it looked at by a pro. Some of the more electonically inclined here may suggest a bit of poking around inside before you do that, depends on what you're comfortable with!

[mohawk1975]

Yeah I never run it in Class A mode -

Logic tells me surely if this is a short circuit or leak to chasis surely it should happen as soon as I turn on to use it ? It seems to happen after a few hours of use - especially when the thing gets a little hot (but hey my knowledge of electricals is really next to nonexistent).

The other thing is - does anyone recommend I attach a wire to the chasis and earth the the thing? The thing shouldn't need an earth but who knows just throwing it out there. Any suggestions would be great. Thanks.

[MikeFaulkner]

I don't think attaching a wire to the chassis will really solve your problem. I think, as posted earlier, there is a grounding problem within the amp. If you are comfortable poking around, unplug the amp from everything, remove the cover and look for connections to the chassis, usually a wire with a lug attached to a nut and bolt, or similar. These should be a tight solid connection.

If all seems ok, then I'm afraid its a trip to the repair shop.

Hope this helps.

Originally Posted by mohawk1975

Yeah I never run it in Class A mode -

Logic tells me surely if this is a short circuit or leak to chasis surely it should happen as soon as I turn on to use it ? It seems to happen after a few hours of use - especially when the thing gets a little hot (but hey my knowledge of electricals is really next to nonexistent).

The other thing is - does anyone recommend I attach a wire to the chasis and earth the the thing? The thing shouldn't need an earth but who knows just throwing it out there. Any suggestions would be great. Thanks.

[mohawk1975]

Thanks Mike - I will open it up and tak a look -

[mohawk1975]

Okay a llittle update - I haven't opened up the Marantz Amp yet - however what i did try (which is very non technical) but I think was a worth experiment was too use the amp for more than four hours straight with a fan pointed directly over the ventilation slots and hey presto the thing did not reset itself or shut down or behave strangley to physical touching it at all - have to say the fan kept the amp relatively cool and not hot as it would normally without the fan.

So conclusion looks like its a over heating issue - but why? surely a device like this should be able to cope with more than 2 hours use without shutting itself down?

Any suggestions guys please? Or do i still need to get a pro to look at it?

[davey42]

Yeah that's a good idea with the fan, I have the same amp and I want to do something with fans and an enclosed hifi rack to create a decent airflow going from bottom to top. I think it's a good idea to keep the amp cool since the life of the capacitors drops considerably when running over long periods of time at high temperatures. But, doing this would create more dust buildup inside the amp (greater airflow through the amp), which would have to be cleaned out about once a year.

On a side note, I had to take the case off my amp recently to get out a small piece of metal foil from a chocolate coin that my son had 'accidentally' dropped in through the holes at the top . I was angry about this, but in the end I was happy because there was thick layer of dust over all the components, which I realised was making the amp hotter than usual (and was a barrier for the piece of foil!) I cleaned it all out and now those HDAM modules shine. The amp is cooler now but I'm still not happy because it gets really hot after a few hours, even in a cold room.

Another crazy way to cool it would be to attach a copper heat pipes to the heatsinks (would have to cut the case) and run these to an external passive radiator on the back or something. I'm not sure if this would cause interference due it being an aerial, but there would be no noise/electrical interference from a nearby fan.

I wonder if one could create a stirling heat engine to physically get air moving driven by the heat of the amp itself? It would reach equilibrium and the amp would be cooler.