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Denon PMA-300V: [Fixed] Right Channel is still audible at 0 volume

Doodski

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catch22

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If you don't mind immersing the entire amp in hot water to melt the dried out beer and then doing the controls clean and lub anyway fly at it...LoL.
you must be joking but even as unskilled as I am, in cleaning I am not likely to confuse the pale ale and the Isopropyl Alcohol :) :) :) so, the very serious question is still open :)
 

Doodski

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@catch22 the entire circuit layout of volume, tone, subsonic, bass and treble, loudness etc are all prone to the most convoluted and diabolical faults as they appear when trying to troubleshoot what is simply a dirty switch/control.... I never troubleshoot before cleaning all the switches and controls... It is imperative you clean and lub before getting techy and diagnosing the circuitry.
 

Doodski

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you must be joking but even as unskilled as I am, in cleaning I am not likely to confuse the pale ale and the Isopropyl Alcohol :) :) :) so, the very serious question is still open :)
haha... I'm enjoying today's chatter at ASR... So much going on and it's all very fast and good stuff.
 

Zapper

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1000003000.jpg

The wire circled in pink is the right volume out. Green is ground. Blue is left volume. Measure pink to green. Loudness OFF, subsonic ON. Measure blue to green for comparison.

R and L are not marked in the schematics, the channels are called a and b - so I might have left and right reversed. Turn the balance knob to check. If you turn it all the way to left, the pink to green resistance should go down.
 
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Doodski

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View attachment 357147
The wire circled in pink is the right volume out. Green is ground. Blue is left volume. Measure pink to green. Loudness OFF, subsonic ON. Measure blue to green for comparison.

R and L are not marked in the schematics, the channels are called a and b - so I might have left and right reversed. Turn the balance knob to check. If you turn it all the way to left, the green pin resistance should go down.
Please refer to this post and follow the instruction..LoL. :D
 
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catch22

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More often than not, my impatience plays bad jokes with me.
I thought this was the case now as well.

What I did: I quick googled that IPA, if not diluted with water, although not as efficient as DeoxIt, but may help. So I took a tiny straw like 1mm dia, immersed into a bottle with IPA and put a finger on, then released into the potentiometer and rotated for a while. It evaporates quickly from the surface, but I also helped evaporation with a fan on mild heat.
I thought, why not, in the worst case I will get a replacement ponetciometer from aliexpress for 5 euro :) It looks exactly the same as in 1980s Denon :)

View attachment 357147
The wire circled in pink is the right volume out. Green is ground. Blue is left volume. Measure pink to green. Loudness OFF, subsonic ON. Measure blue to green for comparison.

R and L are not marked in the schematics, the channels are called a and b - so I might have left and right reversed. Turn the balance knob to check. If you turn it all the way to left, the pink to green resistance should go down.

It's a different measurement now.

Resistance betweenat Volume 0at Volume 20at Volume 40
Green (Ground) to Pink3 Ω8.72kΩ32kΩ
Green (Ground) to Blue98 Ω9.11kΩ34kΩ

compare with my measurements before IPA cleaning
4<--->3 (Green to Blue)2.2k15k37k


And it works! There residual sound is nearly nearly gone (maybe not as new, but one would only hear it in complete silence 30cm from the speaker)
!!!!!!!!!!!!! ;):):p:D:p:rolleyes:
 
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Doodski

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More often than not, my impatience plays bad jokes with me.
I thought this was the case now as well.

What I did: I quick googled that IPA, if not diluted with water, although not as efficient as DeoxIt, but may help. So I took a tiny straw like 1mm dia, immersed into a bottle with IPA and put a finger on, then released into the potentiometer and rotated for a while. It evaporates quickly from the surface, but I also helped evaporation with a fan on mild heat.
I thought, why not, in the worst case I will get a replacement from aliexpress for 5 euro :)



It's a different measurement now.

Resistance betweenat Volume 0at Volume 20at Volume 40
Green (Ground) to Pink3 Ω8.72kΩ32kΩ
Green (Ground) to Blue98 Ω9.11kΩ34kΩ


And it works! There residual sound is nearly nearly gone (maybe not as new, but one would only hear it in complete silence 30cm from the speaker)
!!!!!!!!!!!!! ;):):p:D:p:rolleyes:
Haha... You are too much! RFLMAO.. Well done for now... Make sure you get all that India Pale Ale out so it does not gunk up the works and use some proper control cleaner and lube to get everything spotless inside. Hahaha.. You're a classic. :D
 

Zapper

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More often than not, my impatience plays bad jokes with me.
I thought this was the case now as well.

What I did: I quick googled that IPA, if not diluted with water, although not as efficient as DeoxIt, but may help. So I took a tiny straw like 1mm dia, immersed into a bottle with IPA and put a finger on, then released into the potentiometer and rotated for a while. It evaporates quickly from the surface, but I also helped evaporation with a fan on mild heat.
I thought, why not, in the worst case I will get a replacement ponetciometer from aliexpress for 5 euro :) It looks exactly the same as in 1980s Denon :)



It's a different measurement now.

Resistance betweenat Volume 0at Volume 20at Volume 40
Green (Ground) to Pink3 Ω8.72kΩ32kΩ
Green (Ground) to Blue98 Ω9.11kΩ34kΩ

compare with my measurements before IPA cleaning
4<--->3 (Green to Blue)2.2k15k37k


And it works! There residual sound is nearly nearly gone (maybe not as new, but one would only hear it in complete silence 30cm from the speaker)
!!!!!!!!!!!!! ;):):p:D:p:rolleyes:
Congrats! That shoild do it - button it up and have a beer!

FYI electronic contact cleaner is often available at auto parts stores, since cars have a zillion connectors and contacts in them.
 
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catch22

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Guys you are such incredible help making the weekend more fun :)
@Zapper to understand those explanations in posts #6 and #8 will be my homework for next days :)
@Doodski not IPA unfortunately, but Guinness is waiting :)

BTW why at full volume we are not reading 100k resistance but just 32k/34k? the pot is indeed 100k with marking on it.
 

Doodski

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@Zapper to understand those explanations in posts #6 and #8 will be my homework for next days :)
I'm glad you can glean stuff from @Zapper's far out circuitry analysis because he often went over my head that's for sure...LoL.. Have fun!
@Doodski not IPA unfortunately, but Guinness is waiting :)
Guinness is delicious although I prefer a very dark (Like 6 fills me up goody goody.) caramelly Old English Porter that goes well with pickles and fudge cookies at the same time. Try it!
BTW why at full volume we are not reading 100k resistance but just 32k/34k? the pot is indeed 100k with marking on it.
I'm staying in my lane and expecting a fascinating technique of explaining the answer by @Zapper.
 

Zapper

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to understand those explanations in posts #6 and #8 will be my homework for next days :)
Feel free to ask questions.
BTW why at full volume we are not reading 100k resistance but just 32k/34k? the pot is indeed 100k with marking on it.
Because the top of the resistor isn't open, or shorted. It's connected to the preamp via an active switch (IC3). When the amp isn't powered this will present an undetermined resistance. So what you are seeing is the resistance of the pot, in parallel with the undefined resistance presented by IC3. In addition there are NPNs TR4 and TR5 connected to the signal path. I haven't figured out exactly what they are for, but they appear to be part of bias circuit. You may see the measurements change while you are taking the reading, as the current from the DVM can build up charge in the circuit and turn things on and off.

There are two ways I see to take IC3 out of the picture. I've mentioned the first one already - turn on the subsonic filter. Second is to switch the input to either of the tape playback inputs. You can try those things and measure again.

With IC3 and TR4/TR5 in the circuit, the direction you connect the leads of your DVM may matter. Try reversing the connections and see if the results change.
 

Zapper

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In addition there are NPNs TR4 and TR5 connected to the signal path. I haven't figured out exactly what they are for, but they appear to be part of bias circuit.
TR4 and TR5 are used to mute the signals when switching inputs.
 
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catch22

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Feel free to ask questions.

Because the top of the resistor isn't open, or shorted. It's connected to the preamp via an active switch (IC3). When the amp isn't powered this will present an undetermined resistance. So what you are seeing is the resistance of the pot, in parallel with the undefined resistance presented by IC3. In addition there are NPNs TR4 and TR5 connected to the signal path. I haven't figured out exactly what they are for, but they appear to be part of bias circuit. You may see the measurements change while you are taking the reading, as the current from the DVM can build up charge in the circuit and turn things on and off.

There are two ways I see to take IC3 out of the picture. I've mentioned the first one already - turn on the subsonic filter. Second is to switch the input to either of the tape playback inputs. You can try those things and measure again.

With IC3 and TR4/TR5 in the circuit, the direction you connect the leads of your DVM may matter. Try reversing the connections and see if the results change.
TR4 and TR5 are used to mute the signals when switching inputs.
Thanks again, more food for thoughts :)
 
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