Denon PMA-655R input selector problem

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Hi!


I have a problem with the input selector of my Denon PMA-655R. I bought it second hand and when I got it the input selector switched back and forth continuously when I turned the selector knob.

I thought the rotary switch was dirty, so I disassembled it and cleaned it. This solved the problem of switching back and forth, but now the input selector stops working completely after 5 seconds of use (I cannot change the input). When I power on the amp I can use the input selector normally, but as soon as I let the input the same for more than 5 seconds it doesn't function anymore.
However, if I turn the record selector knob the input selector starts working again (for 5 seconds of use)!

Also, strange thing is: The microprocessor does keep track of the input selector knob even though the input doesn't change. For instance, if I turn the input selector knob to the right two times nothing happens. When I turn the record selector knob after that, the input selector does shift two inputs to the right! So the record selector knob triggers the input selector knob somehow.

I already replaced all capacitors on the input selector circuit and changed IC903 which powers the 5v VCC line. No difference!
Could the microprocessor be defective?

Thanks in advance!

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@Rayma
I don't think it's caused by loose solderjoints, symptoms don't match.. Also tapping the PCB doesn't change anything.

@Mlloyd1
I can make a video if you want, maybe that can clear things up?
All functions work, like the remote (volume up/down, switching inputs), LED's come up at the right input, inputs themselves work...
Only when I try to switch inputs with the input selector knob things go crazy.

@KatieandDad
I will try to change it thanks.
What should I exactly check on the reset line?

Also something to notice, when I turn the input selector one full round the input switches 1 input back instead of forward, and then continues to go forward again. But maybe this is normal due to the design of the rotary switch.. But I'll make a video so you guys can see it ;)
 
What did you use to clean the switch ??? there is some things that cannot be cleaned properly with the available methods to a diyer .

The behavior of the IC when the switch is loose or in general loosing contact with the pin is unknown ...

Try to imitate the behavior of the switch with a jumper wire to see if this is stabilizing the situation

Kind regards
Sakis
 
Okay, it turned out that filthy soldering connections caused the problem..!
Oxidation between some soldering joints created shortening, causing the microcontroller to freak out when shifting the input selector.

I cleaned the PCB with some alcohol and a toothbrush, and now it's working perfectly again!
 
I had the jumping selector issue on my PM 655 R, and resolved it following the guide at

Denon PMA-980R and problems with input selector? Here's the fix! | Audiokarma Home Audio Stereo Discussion Forums

This solution consists in cleaning the track of the selector, which is not easily reached, but the guide above provide detailed steps on how to achieve that (there are some variants depending on the exact model).

Thanks! I used the same advice to fix a Denon PMA S10 II, and it went well. :)
It was even easier, since the switch isn't tied down by an external metal clamp.
 
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