Marantz PM6004

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Have been asked to look at this Marantz PM6004 amplifier, report is it  
"cuts out" if the volume is raised more than a third.

Had a Google and I get hits saying its "a common fault" but nothing  
about resolutions.

Before tearing it apart, are there any common issues with this model?
(I found the auto shutdown "crackle" fix)
What it appears to do, on a dummy load, is the protection circuit is  
kicking in, seemingly at random...

Obviously I'll get in there and measure voltages and waveforms when I  
have it set up on the bench later :)

Re: Marantz PM6004
On 21/05/2017 13:16, Lee wrote:
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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

Re: Marantz PM6004
Lee wrote:

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



.....  Phil  

Re: Marantz PM6004
On 21/05/2017 14:07, Phil Allison wrote:
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I have the Peak ESR70, from your comment I'll be sure to check the caps :)

Re: Marantz PM6004
On Sunday, May 21, 2017 at 7:17:01 AM UTC-5, Lee wrote:
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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.

Re: Marantz PM6004
On 22/05/2017 17:43, Mark Zacharias wrote:
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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.

Re: Marantz PM6004

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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


Re: Marantz PM6004
Lee wrote:

------------

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 ** Are you using a dummy load ?  

    Please describe.  



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 ** Depends on that mysterious load.  


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


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** Your scope should be accurate enough.

   That a secret too?  

....  Phil  

Re: Marantz PM6004
On 24/05/2017 03:16, Phil Allison wrote:

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.

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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.

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See answer above :)

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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**.



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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.

Re: Marantz PM6004
Curent limitation.


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