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.