Denon pma 510ae, static noise in left channel

[kjb]

Ok. Got this Denon pma 510ae amp. It has a low static (white/Pink) noise in left channel, But the music sound fine otherwise. So easiest to hear the noise when there is no music playing. The noise changes when turning the volume knob. Most noise is at about 1/4 volume and 3/4 volume. But when turning on source direct the noise rises more and more the more volume i give it. The signal path is separated in three sections. There are the input section on the main board, and a volume and bass treble balance aso on the front panel PCB connected by i wire . An Its the power stage on the main board. I disconnected the signal wires to the power stage and it became quiet. Its probably not on the main board input side either. I disconnected the left signal wire coming in from the input side and there was still noise. I put another pot parallel to the main pot, no difference. Any ideas what could be the source of the noise? Is it The tone controls?

 

[kjb]

Attached the service manual and a image that shows the area that might be problematic. I think I will have to take the amp apart to check bad solder joints. But all I have seen so far looks shiny and nice. Can The tone contol buffer somehow distort the signal even if its not in the signal path?
Btw. It does not matter how i turn the balance or tone contols. The noise is the same.

 

[duncan2]

You " disconnected the signal wires to the power stage and it became quiet " as its wideband noise its more likely a noisy input side active device or a faulty/overheating resistor and its possible a ceramic capacitor is faulty try paralleling a lower value to check but you also have two big chips involved for controlling functions .

Can you bypass the tone control section signal input/output ?

 

[rayma]

Yes, just use the source/direct switch. Is one position noisy, and the other position quiet?
If so, it's in the buffer or tone sections.

 

[kjb]

Source direct mode is also noisy. Its a bit different as I explained in the fist post. Amplitude of noise changes differently when turning the volume knob depending on the mode.

 

[rayma]

Then it's not the buffer/tone controls.

You may need to ground certain signal path circuit nodes (that have no DC voltage on them)
to narrow it down further.

 

[duncan2]

Then the input side is faulty if you have eliminated the tone section --the resistance of the volume control plus the inputs various impedance's /filters combine to emphasize the noise at various levels ( a peak appears ).

 

[kjb]

I also disconnected the left signal wire coming from the input section on the main board, but keeping the gnd and right signal. And it didn't help. However it's still a resistor and an input capacitor in the signal path after the wire from the main pcb. From that signal goes stright to the source direct switch and then on to the volume pot.

I can try to ground some signal nodes to see if thats gives me any clues. Thanks for the suggestion, will do it tomorrow.

 

[rayma]

Make sure that anything being grounded won'r affect the DC voltage anywhere.

 

[Alexchoi]

could it be the RY52,
just short the pin 3 & 4, and pin 5 & 6,
see if noises go away..

if noises persist,
lift up one leg of R239 0r and R240 0r to cut power supply to the IC20 TL9164, ( use CD, direct..)
and see if it help...

 

[kjb]

I grounded the left channel signal path before the volume pot and the noise remains. When I ground directly after the pot the noice is gone. So I guess the pot needs a replacement. They doesn't seem easy to find 🙁 Part number CVV9Y13B503Z

 

[duncan2]

I have probably picked you up wrong , you say---"when I ground directly after the pot the noise is gone " .

If you are shorting the signal output to earth then the noise "will be gone " .

 

[kjb]

If i short the signal before the pot there is still noise. So the noise must come from the pot or after it?
But there is also a 1k resistor after the pot. And when I shorted the signal before the resistor the noise went away, as it should.

 

[kjb]

Would it be ok to try with a 10k alps pot? The original is 20k. Or is it possible that I'll break something. The TC9162 and the phono stage buffer perhaps.

 

[duncan2]

Go ahead its worth a try if you think that's what causing it , at the very least it will eliminate the control.

Just watch what you unsolder --better still photograph a closeup of the original before you do it so that you will remember the connections.

 

[kjb]

Ok. The bad News is that it was not the vol pot. I replaced it with the alps pot and the noice remained. But its also kind of good because it is really hard to find replacements for it. Search goes on..

 

[kjb]

I flipped left and right signal wires into the power stage and the noice remained in the left channel. I wish I had tried this a long time ago 😱

 

[duncan2]

I didn't think it was the volume control as the type of noise you are complaining about isn't a standard fault on controls ( although other types are ) at least you now know its the left channel and before the volume control section .

I still think its either an active device fault-capacitor fault -resistor feed fault at or near the input as I said in one of my previous posts.

 

[kjb]

Dont know if I misunderstand, I flipped the signal wires after the volume control going in to the power amplifier stage. And the noice remained in the left speaker. Same channel as before So I would think the noise is generated in the left channel of the power stage.

 

[duncan2]

Is what you are saying you tried both the right and left channel inputs in first the right channel and both the inputs in the left channel and BOTH inputs were okay in the right channel but noisy in ONLY the LEFT channel ?