YAMAHA CR-620 Volume Issues

[JB8]

I have a CR-620 that had some channel drop-out issues, was coached to replace the relay (thank you @avionic , and that fixed most of the issue, but I still have low level, balanced volume at the zero position. Since this is considered a separate issue I'm starting this thread.

As noted, with volume pot at zero I'm getting very low level sound from both channels, then when I start to turn up the volume I immediately get a ~60/40 split, heavy on the right side. If I crank it up to 50% the volume eventually equalizes across both channels.

Does this sound like a potentiometer/wiper issue or are there other paths to explore before considering a replacement of the vol/bal pot? Btw, I've cleaned the pot at least three times with Deoxit, making sure to give the pot a full rotation left/right roughly 30 times back and forth during each cleaning and the issue remains.

If a replacement is necessary is there an aftermarket option? These seem to be fairly scarce on the second hand market.

 

[avionic]

Does this sound like a potentiometer/wiper issue

Yes. Have you tried cleaning it yet ?

 

[JB8]

Btw, I've cleaned the pot at least three times with Deoxit, making sure to give the pot a full rotation left/right roughly 30 times back and forth during each cleaning and the issue remains.

Yessir, several times.

 

[Nashou66]

Yessir, several times.

Did that entail disassembly?

Nashou

 

[JB8]

Hey @Nashou66, thanks for jumping in. I was trying to avoid pulling it but ultimately it may be the only and best next step. It will be my first potentiometer surgery, any advice specific to disassembly and cleaning?

 

[Nashou66]

Hey @Nashou66, thanks for jumping in. I was trying to avoid pulling it but ultimately it may be the only and best next step. It will be my first potentiometer surgery, any advice specific to disassembly and cleaning?

I think there was a recent thread of someone doing just that , not sure if it was the same model but they are mostly similar I would imagine.

Let me see if I can find it.

Nashou

 

[Nashou66]

Here are some pics of a volume pot removed and dissasembled . Do not bend any tabs or the likes.

Best not to bend any metal to metal contacts or you can kiss it good-bye..

https://audiokarma.org/forums/index...-pots-with-deoxit.683957/page-3#post-13232415

Best i can do for now, I know I have seen complete threads on this.

Found this thread, its a good guide . Links to a video as well.

https://audiokarma.org/forums/index.php?threads/yamaha-c-60-c-80-volume-pot-cleaning.960917/

Nashou

 

[JB8]

Thank you, Nashou, for finding the links!

I'll check these out and see how it goes along with updating this thread with my findings.

Thanks to @avionic as well, I always appreciate your vast knowledge and availability, an invaluable resource to this forum.

 

[JB8]

Now all I can see is avionic's post about "best not to bend any metal to metal contacts or you can kiss it goodbye"...

So, it's out, but even though I looked at the other cleaning threads I'm stumped as to how I'm supposed to clean it effectively without disassembling it, which would require bending metal to metal parts. Doh!

Btw, testing across the outside volume posts I'm getting ~46K ohms, so I'm assuming that's within normal tolerances for a 50K pot? The "volume at zero" issue, is that because the wiper ends are not contacting the pad in the correct place or, could there be some corrosion preventing proper contact? Sorry for all the questions, would love to figure this out since I've had it happen on other units as well.

Any additional advice would be fantastic.

 

[Nashou66]

Now all I can see is avionic's post about "best not to bend any metal to metal contacts or you can kiss it goodbye"...

So, it's out, but even though I looked at the other cleaning threads I'm stumped as to how I'm supposed to clean it effectively without disassembling it, which would require bending metal to metal parts. Doh!

Btw, testing across the outside volume posts I'm getting ~46K ohms, so I'm assuming that's within normal tolerances for a 50K pot? The "volume at zero" issue, is that because the wiper ends are not contacting the pad in the correct place or, could there be some corrosion preventing proper contact? Sorry for all the questions, would love to figure this out since I've had it happen on other units as well.

Any additional advice would be fantastic.

View attachment 2481272 View attachment 2481273

Do you have an ultrasonic cleaner?

If you do you can fill it with denatured alcohol and drop the volume pot in there and
run it for a few minutes .

But I think that type is a little harder open. Have a pic of the back side and from on?
I would think just from looking at the pic that it come apart from the back to front.
You'd bend the last section tabs open and the back case should come off. then you can see how its all held together .


EDIT: Found this visual instruction guide, they use an eraser on the metal parts but I would use
Alcohol, de natured if possible and a q-tip or foam swab. For the carbon side eraser seems like a good idea, unless some one else here has a better recommendation .

https://www.instructables.com/How-To-Clean-The-Controls-On-Your-Amplifier/

Athanasios

 

[JB8]

No ultrasonic cleaner, so I started taking it apart, carefully, but still wanted to see the inner workings. Balance layer was easy to pull and clean, but now the volume section seems to have a spring/clip in the middle of it that's keeping the sections from pulling apart, not sure how to release whatever is keeping them together. I'm very aware that the tabs are fragile, so I figure I've got one shot at this, after it's reassembled I won't be pulling it apart again.

Jumping back in tomorrow, if anyone know's how to get the two final sections apart please chime in, the more the merrier.

 

[Nashou66]

Can you take a better picture of this back side, I can not see if there is a clip that might hold the back cover on.
If not you may just have to pry it off, moving around the cover so not to deform it.

 

[JB8]

No clips on the back so I started from the front end, something I saw in a few other pics and video's.

I'd also been using Deoxit Red for pots like these but it sounds like it may not be the best for the carbon pads and could actually damage them? Anyhow, once I get it pulled apart I'll treat the carbon pad and wiper contact separately and see if a proper cleaning does the trick! Even if I have to replace the part in the end I'm fine with that, needed to learn about these and couldn't stand the thought of weirdness in the volume pot, no bueno!

Also, when measuring ohms across the middle and left posts on each channel, the front section of the switch ranges from ~48K - 0 when going from full CCW to full CW. The rear pot goes from ~48K to 440 ohms when going from hard left to hard right, so that may be part of the imbalance I'm hearing?

Here are some pics, stoked to dig in more today!

 

[JB8]

After very carefully pulling the base off I found the following failure (see pic), so I'm not confident the part can be salvaged at this point. At least I now know how these are put together, so it's not a total loss.

As mentioned, sounds like some folks feel like Deoxit Red (D5, which is what I used on this specific pot a few times) is actually not appropriate for pots with carbon pads, and that instead, they should be cleaned more carefully with products that don't leave behind any residue. This was via a youtube video where the tech said to clean the pad with alcohol then use a fiberglass brush on the metal ring followed by applying just a drop of the concentrated Deoxit red (D100L) on the metal, and the concentrated Deoxit green (F100L) on the carbon pad. All of this along with trying to now completely remove the friction grease (can be replaced with Deoxit Fader Grease?) the pot would have had when freshly installed.... Or something like that. I have zero affiliation with Deoxit, just explaining what was stated in the video.

Anyhow, thanks again, onward!

 

[Nashou66]

After very carefully pulling the base off I found the following failure (see pic), so I'm not confident the part can be salvaged at this point. At least I now know how these are put together, so it's not a total loss.

As mentioned, sounds like some folks feel like Deoxit Red (D5, which is what I used on this specific pot a few times) is actually not appropriate for pots with carbon pads, and that instead, they should be cleaned more carefully with products that don't leave behind any residue. This was via a youtube video where the tech said to clean the pad with alcohol then use a fiberglass brush on the metal ring followed by applying just a drop of the concentrated Deoxit red (D100L) on the metal, and the concentrated Deoxit green (F100L) on the carbon pad. All of this along with trying to now completely remove the friction grease (can be replaced with Deoxit Fader Grease?) the pot would have had when freshly installed.... Or something like that. I have zero affiliation with Deoxit, just explaining what was stated in the video.

Anyhow, thanks again, onward!

View attachment 2481987

If you have friend with a 3d printer they make be able to make you that part. but maybe first try to use some CA glue . looks like the case may hold it together.

 

[JB8]

To close the loop here, found an OEM part on ebay, installed it, all good and back to normal. Thanks again for your help, always appreciated!