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

On 21/05/2017 13:16, Lee wrote:
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

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

Lee wrote:



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



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



...... Phil

On 21/05/2017 14:07, Phil Allison wrote:
Lee wrote:



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



** 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

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

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.

On 22/05/2017 17:43, Mark Zacharias wrote:
On Sunday, May 21, 2017 at 7:17:01 AM UTC-5, Lee wrote:
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

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.

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?


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

Lee wrote:

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


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.


** Are you using a dummy load ?

Please describe.



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?


** Depends on that mysterious load.


Where it's normally installed, it's paired with some very expensive
speakers


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



*assuming my sig gen is accurate, of course.

** Your scope should be accurate enough.

That a secret too?

..... Phil

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.

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.


** Are you using a dummy load ?

Please describe.

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.

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?


** Depends on that mysterious load.


See answer above

Where it's normally installed, it's paired with some very expensive
speakers


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

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**.



*assuming my sig gen is accurate, of course.

** Your scope should be accurate enough.

That a secret too?

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.

Lee wrote:

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


Phil Allison wrote:


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.

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.


** Are you using a dummy load ?

Please describe.

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.


** Good, I need to know it was 8 ohms AND both channels were tested at once.



Where it's normally installed, it's paired with some very expensive
speakers


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

I have been told they are Kef R300, so not that expensive,


** $US1800 a pair is not cheap.


but I
wouldn't like to be buying them. I don't know if they are good speakers
or not.



** Very compact 3-way, bass reflex with impedance min of 3.2 ohms.

Low efficiency too so needs a decent amp.


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**.


** KEF makes a big deal of the bi-wiring idea in the handbook, there are extra terminals fitted and a link on/off switch.

Complete wank of course.


*assuming my sig gen is accurate, of course.

** Your scope should be accurate enough.

That a secret too?

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.


** Either will have good accuracy.



*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.


** The owner is likely playing the system to its MAX and the wimpy Marantz amp is protesting.



..... Phil

On 25/05/2017 01:25, Phil Allison wrote:

Phil Allison wrote:


** The owner is likely playing the system to its MAX and the wimpy Marantz amp is protesting.
.... Phil



Sure sounds like it.
Thanks for the advice, I appreciate it.

Lee

Curent limitation.

Lee a écrit :
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