How to dissemble this volume POT

[JoeDotCom]

I have another tread talking about the restoration of my Technics SU-8600 (here: Dirty circuit board... how bad is it?)
The problem now is that I need to dig into this volume pot more. I was able to mostly dissemble it and pry it open enough to clean it a bit, however my problem is still there. (left channel is about 50% quieter than the right until you hit about 11 o'clock on the dial then it jumps up to match the right.)

I was able to clean the "rear" contacts since i was able to completely expose them, however, i could not reach the inner contacts and a deoxit bath was not enough. How do I separate the shaft from the rest of the unit so i can get to those inner contacts?


Technics SU-8600 Volume pot disassemble
EWC-F 150K Ohm

Sent using a mobile device.

 

[MR_B]

Can you melt a hole with a hot wire, to gain access, if the housing is plastic?
I put a small one in the side, then another in the other side to allow for blow-thru.

 

[JoeDotCom]

Can you melt a hole with a hot wire, to gain access, if the housing is plastic?
I put a small one in the side, then another in the other side to allow for blow-thru.

i have blow / spray access. with the screws out and the pot unsoldered from the board, i can spread the housing a bout 1/8 inch so i can spray stuff in there (air/deoxit/lube) but that did not help. I need to get in there to see/clean better.

 

[JoeDotCom]

Can you melt a hole with a hot wire, to gain access, if the housing is plastic?
I put a small one in the side, then another in the other side to allow for blow-thru.

Hot wire is an AWESOME tip though. i keep reading recommendations to drill, and then i see concerns about the debris getting into the pot. MELTING a hole sure would solve that issue: no chunks of plastic floating around.

 

[sonci]

Thats similar to an Alps potentiometer, I have a feeling you should replace it,
anyway, are you sure that volume pot is the culprit?
I had a similar problem, still havent figured out..

 

[JoeDotCom]

I am exploring replacements. It does not seem to easy too find that exact pot anymore. I still need to learn a bit before I will know if i can simply find another dual gang 150K ohm pot.

It is also my plan that next time i take this pot out to tinker on it, to connect a multimeter and see if the resistance measurement displays the same "jump" that the volume does as i spin the dial. If it does NOT, then i will expect the problem resides elsewhere. (that is assuming you can measure resistance of a pot while you rotate it and see a steady decrease in resistance as the pot is rotated. I have not tried it yet.)

I want to clean / inspect that 2nd layer of the pot to rule out any physical damage.

 

[BinaryMike]

It's been way too long since I did anything like this to recall details, but I think you can get it apart by grinding away the swaged portions at the rear end of the control shaft. You should be prepared for the possibility of a bad outcome, because these pots were never intended to be serviceable.

 

[rpeter46]

joe-
Thank you for the documentation. I have the same problem with my 8600. I can notice the difference between the two channels just by looking at the drivers while under power. I'm watching closely!

 

[qsaudio]

I just crack them open, nuts stay on, to get cleaner in, works good.

I don't think I ever desoldered a control in my life to clean them, makes no sense.

But I am of the CFC generation, all this stuff with lube in it is not my style at all. only lube AFTER you clean it.

Here is a tip for everyone, get a bic lighter, heat the plastic spray tube and stretch it, get a razor blade and slice it for a nice thin nozzle opening.Too small it will pop the straw off the can.

 

[JoeDotCom]

ok, I sat down with my DMM, my laptop, and a case of patience (and a glass of Clos Du Bos)

I setup my meter and measured each "notch" in the pot. Plugged that data into a google spreadsheet and bang: a spreadsheet that shows exactly what I was hearing. up until step 10, there is about 3K Ohm difference in resistance then they snap together.

that POT is shot. Any input on options for replacement?

Can i just simply buy another 4 pin, 150K Ohm, stereo Audio Pot?

 

[Watthour]

Does that little circuit board have any function other than to make a convenient connection point for the shielded cables? If not, a standard dual 150K/2W with a log taper might work nicely. The difficulty might be in getting the correct stem length and splines, then getting all of that with detents.

On a separate but similar note, I may have found a work-around replacement for the speaker selector wafers on Kennys. If it works, I'll let you know as well as posting it in the "Wood Forum.

 

[Tinman]

I have had very good results cleaning pots in an ultrasound tank.

Get a small cheap one for jewelery and try alcohol. Then blow dry or just allow it to dry. Follow up with a TINY amount of deoxit (it wicks itself inside) and finish with some fader lube.

Marc

 

[JoeDotCom]

Does that little circuit board have any function other than to make a convenient connection point for the shielded cables? If not, a standard dual 150K/2W with a log taper might work nicely. The difficulty might be in getting the correct stem length and splines, then getting all of that with detents.

On a separate but similar note, I may have found a work-around replacement for the speaker selector wafers on Kennys. If it works, I'll let you know as well as posting it in the "Wood Forum.

Good to know a standard pot may work. I would hate to lose the great feel of the original POT, but i would rather the amp be usable. So that may be an option, even if there are no notches or if the notches don't line up w/ the faceplate markings.

Good to hear about the Kenny selectors. That baby is actually saving the day over at a friends house right now, so it has more than served its purpose and still going strong!

I have had very good results cleaning pots in an ultrasound tank.

Get a small cheap one for jewelery and try alcohol. Then blow dry or just allow it to dry. Follow up with a TINY amount of deoxit (it wicks itself inside) and finish with some fader lube.

Marc

interesting. would that help even if the area in question is stuck inside the case? I am pretty sure the bad section is the one in the "middle" of the setup, so it is the area that i cant get inside to scrub. would a non-ultrasound alcohol soak work nearly as well? (what kind of alcohol are we talking about there?)

 

[rpeter46]

like a surgeon...

Joe,
You are already considering replacement if you can't get it clean. Have you considered "removing" the outer part of the plastic enclosure on one side? In other words, cut along the red lines and remove one "panel" of the plastic boxes that enclose the pot? Like this...
.....

If it can be accessed and cleaned, THEN you can cobble together a way to keep it dust free(you'll come up with something...)

notice how carefree I am with cutting open YOUR 8600? :yes:

Paul

 

[rpeter46]

Joe,
You are already considering replacement if you can't get it clean. Have you considered "removing" the outer part of the plastic enclosure on one side? In other words, cut along the red lines and remove one "panel" of the plastic boxes that enclose the pot? Like this...

https://skydrive.live.com/?sc=photos&cid=c9d95efeee04fc57#!/?cid=c9d95efeee04fc57&sc=photos&uc=1&id=C9D95EFEEE04FC57%21158!cid=C9D95EFEEE04FC57&id=C9D95EFEEE04FC57%21163&sc=photos
If it can be accessed and cleaned, THEN you can cobble together a way to keep it dust free(you'll come up with something...)

notice how carefree I am with cutting open YOUR 8600? :yes:

 

[JoeDotCom]

Joe,
You are already considering replacement if you can't get it clean. Have you considered "removing" the outer part of the plastic enclosure on one side? In other words, cut along the red lines and remove one "panel" of the plastic boxes that enclose the pot? Like this...
If it can be accessed and cleaned, THEN you can cobble together a way to keep it dust free(you'll come up with something...)

notice how carefree I am with cutting open YOUR 8600? :yes:

Oh me likey! I was thinking that if i am willing to replace it i may as well really dig into that pot and go into "clean or destroy trying" mode. I like your cutting idea though, it may allow me decent access without destroying the structure of the POT case.

thanks for the tip!

 

[rpeter46]

you could use some kind of heated tip to 'melt' your way to success instead of a cutting process that creates little plastic scrap...

 

[JoeDotCom]

you could use some kind of heated tip to 'melt' your way to success instead of a cutting process that creates little plastic scrap...

Good call. I have a weller butane soldering iron that has a hot knife attachment. I was always wondering how I would put it to use. I think i may have an idea now. (definitely outdoor/garage work here.)

**If i wanted to be a real thug i would just use pliers and snap that part off clean. (though with my luck it would likely just shatter.)

 

[JoeDotCom]

So, i got inside to the rear POT assembly. It did not look too bad, but i cleaned it and inspected and all looks fine. My meter still shows the jump around click number 10. and it still sounds like crap when i wire it back in.

As a "quick" fix, can I go buy this $4 100K stereo volume pot at radio shack?
http://www.radioshack.com/product/index.jsp?productId=2062359#

-I cant see the pins, what if it does not have 4 pins like the existing pot?

-Also, would I need to also wire in a 50K resistor with each side of the pot to make it match the original 150K? (I dont care if i lose out on some volume range, I would never play it above 50% anyway.)

 

[AK 47]

mine was exremely noisy, did this, quiet as a mouse:thmbsp:

http://analogattitudes.freeforums.org/technics-su-8600-volume-de-ox-by-drilling-t207.html