Kenwood Basic C2 Volume Pot Issue

Andyman

Scroungus Stereophilus
Subscriber
Well, my C2 saga continues...

About a month ago, I dug into the C2 and pulled the Balance pot as I was having issues. I did add the 2 resistors, but used 220K instead of 185K as that was the closest I could find at Radio Shack.

It worked better, but I was still getting some volume drops and irregularities, especially when wiggling the volume pot shaft. I messed about with the ribbon cable from the Balance board to the Volume board and found when I held it in the center and wiggled either side that the Volume side gave issues, but not the Balance side. so I reflowed the connections in hopes of curing it, but it still arose.

FF to yesterday. I found my mini screw drivers and went into the Volume pot to clean it. I managed to remove the rear cover far enough to get some Deoxit on the rear wiper and plate, and reassembled it after working it about. It worked, but after some variances it settled down to a smoother, but lowered output.

Today I fired it up and it sounded fine, nice and clean, for about 45 seconds and then it dropped down about 10 dB or so all of a sudden.

Any ideas? The drop after turning on makes me wonder if there's something more to this than simple mechanical issues, like bad caps or transistors?

Any and all help is appreciated!!
 
OK, so 2 years later an update and reboot.

About 2 months ago I determined the issue wasn't in the Balance circuit, but in the volume pot itself. I was able to open the back up a bit and DeoxIt the works and it worked quite nicely up until a few days ago. Now it drops in and out and sometimes gets quite a bit louder. Doing some research, it appears I may be able to rebuild it, but I'm wondering if anyone has replaced one and if so with what? I'm not a tech, but reasonably handy, so i'm willing to give it a shot.

That being said, a replacement isn't easy to find as it's a 4 gang ALPS unit, a blue Velvet variant I believe, and I'm not able to find a plug and play replacement. Here's a pic i borrowed, it's the big unit in the upper right.

30926408386_1f380c69ef_k.jpg



And here's a pic of the back of mine.Any ideas on what I can replace it with??? It looks like a 4 gang RK27 but with 2 3K legs and 2 56K ones??

20170328_191146[1].jpg
 
I don't think spraying through the back will hit all 4 sections of the pot.

Would desoldering the pot and removing those screws allow everything to slide apart?

What I have done in the past is very carefully drill a hole top centre of each section just large enough to get some deoxit in there. Drill VERY CAREFULLY and slowly with almost no pressure as you don't want the bit breaking though into the pot. Melting through with a fine tip soldering iron might work, too.

Flip the unit over to let the deoxit drain/dry. Cover the holes with a bit of hot glue or electrical tape.
 
Maybe later this weekend. I finally giked my taxes and can focus now on finishing up some works in progress.

Stay tuned!!
 
OK, another 2 years passes and I need to use this pre again, but the pot still is funky. This time I notice that the pot does kick in with a little downward pressure on the shaft and before I noticed that pushing on the board sometimes helped too. Based on this, I decide to reflow the solder joints and see if that helps.

After a bit of digging to find out how to access the underside of the board, I get it all apart and reflow the 12 connections, all which looked OK, and give her a test. Works like a champ. Played for 3 hours with zero problems! I am a happy camper.

I was ready to do some of the upgrades on it, but there are a few other things I need to attend to first, so I'm buttoning her back up for work in a month or so. Plus I need to dig through the C1/C2 threads to assure I'm doing the right upgrades. But it's working great and ready to go.

Earlier today I opened up my Yamaha C-70 and was able to get the ALPS pot on it open enough to squirt in some DeOxit and remedy another dropping volume pot so I'm batting 1000 today and 2-0 on preamp volume pot repairs.

This is good!!
 
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