Marantz PM6004

Before "tearing it apart", measure the main rail voltages, with a dummy load. Going out of balance with some drift of bias somewhere is my guess, then the protect mode cuts in

** You do own an ESR meter - don't you ??

..... Phil

I have the Peak ESR70, from your comment I'll be sure to check the caps :)

I would check to see if the output waveform for either channel clips prematurely; this is seen by the protection circuit as DC voltage.

Also check for bad solder connections involving the output transistors.

I would also check to see if the integration capacitor for the protection circuit might be open. In this case maybe C9003, a 47uF at 50V.

A good multimeter and oscilloscope are generally required to trace down these faults.

Right, I am now confused. Not that it's difficult :)

I think the original music source it was tested with was severely over driving it...

If I feed it a 0.8v pp sinewave from my sig gen it doesn't clip at full volume and doesn't go into protect. If I feed it 1v pp it just starts clipping (symmetrically) at 75% volume then "soft" protects if pushed to "full" - that is it goes into "mute" (blue led) and lowers the volume then un-mutes itself. It has a motorised volume pot so you can see it do this :)

However, if I feed in 2v pp* (max it says in the specs), then it *just* starts clipping at half volume and if pushed further to about 75% volume it goes straight into standby with "protect" (the standby led) flashing, needing a power cycle to reset.

Other than it being a touch quick to go into protect, does this sound like it's actually working properly? Or at least as it was designed?

Where it's normally installed, it's paired with some very expensive speakers and I am loathe to poke about in the protection circuit. If the advice here is that it's behaviour is still flakey then someone else can take that risk :) :)

*assuming my sig gen is accurate, of course.

does the protection circuit sense the current i.e. voltage drop across the emitter ballast resistors?

have they changed value?

is the quiescent current correct?

m

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** Are you using a dummy load ?

Please describe.

** Depends on that mysterious load.

** And we are not allowed to know their identity either?

** Your scope should be accurate enough.

That a secret too?

.... Phil

snipped for readibilty.

After asking the guy for more info about the speakers, as you asked what there were, I now suspect the problem is his end* and he's getting it back as it is.

But details anyway, since you asked.

I was using a pair of 8 ohm 100W standard metal cased cermet WW resistors on a big metal plate. One for each channel, obviously.

But it does the same with a pair of cheap Gale 3010S speakers as well.

See answer above :)

I have been told they are Kef R300, so not that expensive, but I wouldn't like to be buying them. I don't know if they are good speakers or not.

He runs them bi-wired, apparently. Personally, I fail to see why running two pairs of cables to the same speaker from a paralleled pair of output posts on the *same channel* makes any difference. But I'm sure it must or they wouldn't do it :) I have asked the guy to double check the wiring for problems**.

The one I'm using for this is an old analogue Leader LS8050 50Mhz crt scope. I do have a modern Rigol digital 'scope as well fwiw.

*Apparently, according to the guy, it's been "trigger happy" from new, but it's been "more sensitive" after a recent speaker move. ** So I suspect the speaker wring, but he's plenty capable of sorting that out.

I'm not interested in trying to deal with a potential design/build issue. If he wants it modified he can find someone else to do that.

Curent limitation.