Denon PMA 2000R - sound issue when using tone controls

[ChuckDog]

Hi, I have own this amp since early 00s. Really like it but it has sound problems. When I press Source Direct, the sound works.
When I use the tone controls, the sound is weaker on the left channel and on the right channel the level of sound (amplitude) varies
And sometimes the sound crackles.

Any idea what could be causing this issue?

Br CD

 

[picowallspeaker]

When I press Source Direct,

That is a switch, or better, a diverter (?).
multiple switches/ diverter ( there's an acronym for that...) And activated by the single button/lever, for stereo you need at least two, so it's 6 contacts, the bridge ( or printed on PCB board in rotary knobs) is metal on plastic slides....all this to say that probably the problem is oxidation!

 

[ChuckDog]

Thanks for the response. The source direct is a button and the tone controls are standard adjusting buttons bass trebble.
I will try to find a good oxide clean and check where to spray and see if this will make any difference.

 

[ChuckDog]

Please note though that the sound issue is like this without me using any knobs.

 

[Extreme_Boky]

It seems that source selection is done via relays; however, source direct is done via a switch, as @picowallspeaker mentioned. The switch should be removed, pulled apart, and cleaned until the contacts and little gliders are shiny again. Maybe it's best to give it to someone who specialises in these things... especially if you haven't done something similar before.

The tone control uses one OPAmp and it sits on + and -16V DC rails, stabilised by a nice little voltage regulator section. Those (OPAmp and voltage regulator transistors & Zeners) can also be easily checked... but I believe the issue is with the source direct switch.

I have attached the service manual... good luck.

 

[ChuckDog]

Thanks for the doc and the description. At this point in time I am gathering information to decide if it is worth handing the amp in
To a repair shop. Based on this description it seems like a minor fix for a pro. I have a good repair guy that I handed my beloved Pioneer plasma to. I will contact him and see if he is up to handling this type of repair work.

Strange though that a switch like this could have these impacts on sound but I do have noticed that when pressing the switch the sound varies as well. Ie while I press the button, like a glitch.

 

[picowallspeaker]

The glitch is when the switch moves and the contacts produce noise seen as DC impulse ( no, that's not the scientific answer)
The Rotel RA 971 MK2 in front of me does that as well. Yes, it's my parents amplifier and I proposed myself to clean it years ago but as long as it sits in its Off position nobody cares. So the technician's request might sound strange in a DIY forum...but that's how it goes

 

[ChuckDog]

I will disassemble it later today and check the source direct button and try to clean it but no more than that.
I will keep you posted.

 

[madis64]

and check the source direct button

You could post a photo of the switch.

 

[ChuckDog]

Hi I will do that. I didn’t open it yesterday. Need a good electronic spray, cleaner before I start.

 

[ChuckDog]

Hi, I have been busy with work and also using my Onkyo instead. I connected the Denon today and it followed the same error as above but now with a difference.

After several ours the sound of the left channel was completely gone, this regardless if Source direct is pressed or not.

This seems to point to soldering?

I will contact the repair guy but wanted your input before I call him, should you have any ideas.

 

[ChuckDog]

I let the amp cool down and now the sound is back…. The guy did not have time right now so I will try clean it myself.

 

[a007udio]

I have similar problem, but it seems that my button is physically damaged. Is there any source to buy new one?

 

[ChuckDog]

The part in white seems to be the one connected to source direct. It seems to be soldered to the unit.
I dare not going any further….