Tone pot still not working

Ron Victoria · Post by **Ron Victoria** » 23 Nov 2004 1:56 pm

I checked the "caps" and they build up on the meter. As they are the wax type, the ends aren't blown, so I assume they are good. I changed the tone pot with a new 250K. Now the sound cuts out when you turn it. With the old one in, the tone remained the same. This is an Epiphone Electar. As I said in the other post, the pot is marked 20 M-Z. Someone responded that a 250K would work. I'm now thinking that way back then they used a pot with a different rating. Any suggestions? The Guldan I also just bought does the same thing, cuts out when you turn the tone knob. The "caps" in this one also test and look ok. Whatever the problem is, they both have it. Any sugestions? Thanks, Ron

Ron Victoria · Post by **Ron Victoria** » 23 Nov 2004 2:10 pm

Sorry, should read 200 M-Z

jerry wallace · Post by **jerry wallace** » 23 Nov 2004 2:55 pm

Ron how are the caps wired into the pot?..There are several varations that will work.. But its like this, one end of the cap must go to ground threw the tone pot..

Thats how the tone is changed by grounding the cap or having the pot resistance between the cap and ground.

Again there are several varitaions that will work..One end of the cap can go to the volume pot then the other over to the tone pot.Or you can just have a solid jumper wire from the volume pot over to the tone pot.

But both pots must be connected and the cap resisted in and out of ground by the tone pot..

Hpe this makes since!!

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Jerry Wallace/TrueTone pickups-2001 Zum: D-10,8+6, "98 Zum: D-10,8+8,Nashville 1000,Session 500 ,Session 400 head only amp,Tubefex,ProfexII, Artesia, New Mexico
http://www.jerrywallacemusic.com

Dave Grafe · Post by **Dave Grafe** » 23 Nov 2004 3:14 pm

Did you ever measure the resistance of the old pot (outside post to outside post)?

Normally 200M-Z would mean "200 MEGA (200,000,000) ohms - Z (audio) taper" - if your volume pot is still a 200M then your 250K tone pot could essentially be passing the bulk of the signal to ground as you open it up and thus causing it to cut out.

250K IS a standard value for most modern pickup harnesses but might not be appropriate for a super high impedance unit. I will look up some old drawings and see if I can find anything that will help you out here.

Dave[This message was edited by Dave Grafe on 23 November 2004 at 03:16 PM.]

Ron Victoria · Post by **Ron Victoria** » 23 Nov 2004 3:24 pm

The caps are pig-tailed and connected to the volume pot. One cap goes to ground, the other goes to the tone pot. I'm assuming nobody messed with the circuitry. Could there be a cold solder joint even though it looks ok? Would a continuity pick this up?
Thanks, Ron

Ron Victoria · Post by **Ron Victoria** » 23 Nov 2004 4:05 pm

I just spoke to a person at the electronics store. When I told him the volume cut out on the 250K pot, he said it's too big and that 200 is 200 ohms and the M-Z has something to do with other specs, maybe temperature. He had a 150 which he said will work. He was very knowledgeable. Does this sound reasonable?

Dave Grafe · Post by **Dave Grafe** » 23 Nov 2004 6:49 pm

200 ohms is definitely not enough.

Ron Victoria · Post by **Ron Victoria** » 23 Nov 2004 7:03 pm

When I checked it with the meter, it was still wired in. I forgot the rest of the circuit will affect the reading. I will take it out and then know for sure if it's 200 or 200megs. I did some checking around and couldn't even find anything that big.

Dave Grafe · Post by **Dave Grafe** » 23 Nov 2004 7:40 pm

Here we go, from "The Electric Guitar Handbook" by Jack Darr (1977) - common practice with a single pickup is to use matching 500K audio taper pots for volume and tone (low-pass filter) and wired thusly:

I hope this helps

Dave[This message was edited by Dave Grafe on 23 November 2004 at 07:48 PM.]

Blake Hawkins · Post by **Blake Hawkins** » 23 Nov 2004 9:25 pm

Ron and Dave:

In some old electronic notation M = 1000.

I realize that some use M as "meg" but in the case of this pot, I'm sure that the
200M is 200,000 ohms. The "Z" is either the tolerance or the taper.
Since others have covered the proper connection of the circuit I won't go into that.
However, if the value of the cap is higher than .05, then it will kill the audio signal at one end of the range.
I have a Harmony lap steel that came to me with a switch and a cap in the tone circuit.
The cap (and it looked original) was a .1 mfd which pretty well killed the output of the pickup. I changed that to .022 mfd and had something I could use.
Be sure your replacement pot is an audio taper as has been mentioned in one of the other replys.
Even though the ohm meter shows a charge on the cap, it could still be bad because of a change in the capacity.
What we are dealing with here is a piece of antique electronic gear. It is very different from what the young guys in the electronics stores are used to seeing.
Oddly enough, music stores are more likely to have a correct pot than the corner Radio Shack.
I have bought 250 K volume control pots from Sam Ash Music. I believe Guitar Center also has them.
Blake[This message was edited by Blake Hawkins on 23 November 2004 at 09:56 PM.]

John Bechtel · Post by **John Bechtel** » 24 Nov 2004 12:21 am

I found my Ernie Ball 250K Audio-Pots at the same Fender dealer where I bought my ’65 Re-issue Twin–Reverb Custom™ 15” Eminence and I use them along with a .0224 disc-cap. There is no gr. preference on a disc-cap. I wire it, in either direction; between the Center-(Out) Terminal of the tone-pot and the Lead-(In) Terminal of the Vol.-pot. then connect the Ground-terminal of both pots and on to the ground-(output jack) of the guitar. This combination affords a nice gradual transition between Bass and Treble on the Tone-Pot, for me!

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“Big John” Bechtel
’49/’50 Fender T–8 Custom [X2]
’65 Re-issue Fender Twin-Reverb Custom™ 15”
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Ron Victoria · Post by **Ron Victoria** » 24 Nov 2004 5:27 pm

Go figure, the 200 M-Z lettering on the pot must have been a manufacturer code. I took the pot out and it checked 500K on the ends and defective. I picked up a new one at Sam Ash and will solder it in tomorrow. Hopefully, that's the problem.

Blake Hawkins · Post by **Blake Hawkins** » 25 Nov 2004 4:19 am

Good shot, Ron!

At least we all tried. Glad you've solved the mystery of the pot value.

Blake

Ron Victoria · Post by **Ron Victoria** » 25 Nov 2004 6:23 am

Well, I put the new pot in and it cuts out when turned the other way. The only thing left is a bad cap. I will forge on. Thanks for all the help.
Ron

Ron Victoria · Post by **Ron Victoria** » 25 Nov 2004 4:35 pm

It was a bad cap besides the pot. It works fine now. I am sure I will find the same problem with the Harmony as it's doing the same thing. Ron

Ron Victoria · Post by **Ron Victoria** » 26 Nov 2004 5:17 am

I got the Harmony working also. Again, it was a bad cap. Thanks for all your help. What a great place for resources!!!

Ron