Yamaha CR 640 Volume Pot

Hello,

I have recently picked up a Yamaha CR 640 in great cosmetic shape for $60. Initially, turning the volume control put a lot of static into the right channel, which was intermittently working. One application of DeOxit to all of the pots cleared up the problem, and the receiver sounds gorgeous. About two days later, I am noticing a little static returning when adjusting the volume.

Three quick questions:
Is this to be expected, and might another round of DeOxit solve this?
Is it time to replace the volume pot?

If I need to replace the pot, I'm not entirely sure what to use. I consulted the parts list in the service manual which (I think) listed the part as "VR602 volume 20 KB", part #HC 31 06 80. Googling these brought me no joy, nor did my first attempt at searching these forums.

I'm not a pro or even a seasoned amateur at audio repairs, but I've fixed a few solder joints and replaced a volume pot on another amp of mine, so I imagine that I can succeed , if needed, as long as I can find a suitable replacement part.

Any suggestions would be greatly appreciated. Thanks!

Mike

PS - I'm not near my gear at the moment, so I wouldn't be able to respond to some questions until tonight or tomorrow.

First try another few rounds of Deox-it on the volume pot. To acquire the correct potentiometer your probably going to need a parts unit part. Look up the part # for a CR-820 volume control in a service manual. Someone is selling one on the bay.
Search Yamaha parts ( under consumer electronics ) on ebay.

In my experience (which admittedly is more limited than many folks here), those old pots can require a lot of applications of DeOxit and/or other cleaning agents. I remember the first time the tech/repair guy I take my stuff to showed me all the gunk that came out of the pots of my Marantz 2230 - AFTER he'd already cleaned the hell out of it the week before. And even after that, there was one switch I had to hit a third time myself.

He also said that the problem can come back if you don't regularly use the pots or switches in question. So for example an input selector can act up again if you routinely listen to just one or two sources.

Your pot could be toast or on the way out, but if it seemed to be 100% after a cleaning, then it's likely that more dirt is the issue, rather than the pot itself going.

Thanks to you both!

I'll go back to the deoxit a few more times before I start worrying about replacement parts.

Cheers

I consulted the parts list in the service manual which (I think) listed the part as "VR602 volume 20 KB", part #HC 31 06 80.

Click to expand...

According to Hoyle ( schematic) VR501 is volume control --- 50KΩ X 2
VR601 is Balance control --- 20KΩ X 1

Best to verify visually that either 20KB or 50KB is printed on the volume potentiometers case.
The SM parts list is kind of iffy. Maybe lost in translation or something.

I'm a big advocate of Peavey Silent Slider. It's a cleaner and a lube and actually works very well the first time rather than what seems like is multiple applications of Deoxit.

I just picked up an R300 that had no output of the right channel and nothing but static out of the left. One application of the SS and all of the switches and pots work perfectly.

mphmtn said:

Thanks to you both!

I'll go back to the deoxit a few more times before I start worrying about replacement parts.

Cheers

Click to expand...

Hello

Can you post a picture of your defective pot ?

Yup. I visually verified that VR 501 is printed on the circuit board. I took a few (not very good) pics of the pot. I'll try to upload them later today. I've applied round two of contact cleaner, and the static has cleared up again.

I'll have to keep an eye peeled for the Peavey cleaner.

Thanks again for the help, folks.

Cheers

I visually verified that VR 501 is printed on the circuit board.

Click to expand...

That does help much. Need to visually check whats printed on the potentiometer not the PCB.

Hello

That's why I asked for pictures

I'm not convinced that these photos will be helpful, but here is what I could get without disassembly.

The second round of contact cleaner is currently effective, the the noise is persistent after additional applications, I'll disassemble a little more and post pictures and descriptions of a closer inspection of the pot.

Thanks again.

Mike

Just thought that I would follow up, in case anyone had the same question later.

The volume pot is still nice and quiet after the second dose of deoxit. I got a better photo of it when I was replacing the lamps. It is indeed a 50k ohm x 2.