Denon PMA-2000R Intermittent No Sound to Speakers

[jerdobi]

This is an interesting sometimes works, sometimes won't.

When the amplifier is on the bench it works fantastic. I button it up and play it in my rack with no issues. 24 hours later, power on and hear the power relay kick in, red led blinking for a few seconds and then goes full red; but BOTH power relays are disengaged. I've tried a bit of bumping and no response. (repeat this paragraph 2-3 times ).

Take it back to the bench and see same issue. Decide to look at the protection board behind the bottom cover.

I turn the amplifier upside down remove the bottom to look at the protection board. It looks good with no noticeable issues, all capacitors are high quality caps with no bulges. Well, turn it on while upside down and low a behold it starts working. Put back the bottom, flip back right side up and still working.

My diagnosis is there's a loose connection, but can't see it as this thing is solid with literally no loose wires, just connectors. Whatever the issue, it shuts down both channels and I don't think it's a relay.

Anyone seen this symptom on a PMA-2000R or PMA-2000IVR? Maybe they work better upside down?

Thanks!

 

[sgrossklass]

Could be as basic as a bad solder joint in the wrong place.

I'd say find out how to best measure output DC offset on both channels (pre-relay, of course), and then proceed to do so while reproducing the fault. Either both channels are fine (then you can go on looking in the protection circuit), or one is acting up, then take a loupe to that. Quite literally so - you might find a resistor or transistor leg that is barely even attached. Those wielding the soldering iron on a daily basis have occasionally resorted to bulk resoldering in such cases, especially when there are indications of numerous dubious joints.
With some bad luck, it could also be a hairline crack in the PCB - any indications of the unit having sustained a drop? If found, epoxy board and bridge affected traces.

 

[jerdobi]

The bias on both channels is spot on when reproducing the fault. The speaker relays that are on each amplifier board are just not energized. By picking up the case and flexing it from the opposite corners will fix the issue.

Yesterday, I pulled the protector board and touched up solder joints on each of the 8 connectors and re-installed. Since then the fault has not appeared again even after leaving the amplifier overnight to cool down. I might have fixed it.

 

[Max Martin]

Was that the fix? Have similar problem with same amp, relays doesn’t engage but nothing wrong with R/L channels.
Pain in the butt to get to bottom plate though

 

[jerdobi]

Yes, the fix was to resolder the CN5E and CN5F ribbon cables that are directly soldered to the board (there's no connectors). The ribbon cable is long and not secured and flops around stressing the solder joints over time or when the amplifier chassis has some shock.