Push-Push Tone Pot with no change in tone

[bluesman13]

Hello all and Happy Holidays,

I've wired my Tele using the attached wiring diagram. The control plate with the pots and selector switch (and wiring) was removed from another guitar (where everything worked fine) and wired into this one. The volume control and the selector switch work fine, but there is no change in tone on the push push tone pot which otherwise works fine (i.e. the push-push control works fine). The only wires that were reconnected are the grounds from the pickups and body/bridge grounds, the pickup wires, and the output jack. One thought I had is that I put self adhesive shielding in the control cavity which has limited space for the pots and switch (I reversed the controls so the selector switch is in the back, the push pot in the middle, and the vol pot closest to the neck pickup) is touching some thing and shorting it out, but if that were the case, would the tone pot work at all?.  Several thoughts I had: one of the pots or selector switch is touching the newly installed shielding in the cavity and is shorting something out; the pot is bad; the capacitor attached to the middle lug of the vol/tone pot is bad...

Would someone kindly help in diagnosing the problem?

thx, Steve

Edit: I removed the control plate from inside the cavity, and the problem is the same, so I'm going to assume that my cavity shielding is not causing the problem

[sumgai]

Dec 30, 2023 14:38:10 GMT -5 bluesman13 said:

... but there is no change in tone on the push push tone pot which otherwise works fine (i.e. the push-push control works fine)

I'm having a little trouble parsing that sentence.  All I can come up with is that if the p/p switch works fine, that leads me to believe that there is supposed to be no change in tone.  But if there is supposed be a tonal change, then the p/p switch is not working fine.

Which way should I jump, bluesman13

BTW, a truth table for that diagram would be nice (for both the pup selector and the p/p).  My first impression is that somebody dropped a tab of acid, then commenced to molesting a poor innocent sheet of paper. IOW, deucedly little makes any sense to me, I need clarification here.   

If you please, of course.




sumgai

[bluesman13]

sumgai,

thanks for your response. I'll try to be more specific, but just to clarify, I'm just a wannabe electrical person - I know maybe enough to be dangerous 😃

In reference to your question about the p/p tone pot, I had to go back and check it as I wasn't sure that I reported the correct information. With the selector switch in any of the three pickup positions (neck - bridge/neck - bridge, turning the tone control, does not alter the tone. When the selector switch is in the middle position, when the pot goes from down to up, it makes a "clicking" sound, and the volume gets louder. I'm presuming that that part of the pot is working correctly, even though turning the tone knob in any of the three positions, produces no change in tone. From what I read, the way the push-push control works is, in the down position it's not active. When in the "up" position and the selector switch is in the middle position, it changes the combined neck and bridge pickup from parallel to in series (that's what I read anyway). regardless of whether the p/p pot is "up" or "down", it is inactive when the selector switch is in positions one and three.

As I'm not a knowledgeable electronics person (I'm learning though), it appears that the p/p pot is divided into two parts: the normal three lug pot, and then the additional part, that, I assume, is the part that switches the pickups from parallel to series. I attached a blowup of the pot from the diagram I posted. Is it possible that the p/p function of the pot could be functional, and the tone part of the pot would not work?

I agree that the wiring diagram I attached is not great, but I used it to wire my telecaster originally, and it does work - but (as I posted in another thread), the left handed version of the diagram, contains an error. I did confirm on my own left handed Tele AmPro II that the actual wiring was correct, in spite of the mistake on the wiring diagram that Fender supplies in their user manual.

While i was figuring that out, I replaced the .22uf capacitor that connects the vol pot outer lug to gnd and the tone pot middle lug with no difference. I also connected my multimeter to the middle and outer lug of the tone pot, and it is reading around 250k, so I assume that the pot is functional? I'm going re-soldering all the grounds with the hope that when I reconnected everything, but no difference...

I'm not sure what else I can try?

[mikecg]

Hello bluesman13,

With your multimeter connected  to the middle and outer lug - as before - turn the tone pot from one end to the other - the meter reading should read 250k at one end and close to zero at the other. If it reads 250k regardless of the pot setting - the pot is BROKEN!

[bluesman13]

Hi Mike,

thanks for the tip. The pot does not give a reading on my multimeter when it is connected to the middle and outside lug of the tone pot. Not sure why that is, but anyway...however, I do get a reading if connect the two outer lugs of the pot to the multimeter, but I suppose that doesn't matter? thanks, Steve

[mikecg]

Happy New Year!

And it sounds like you need a new tone pot!

[bluesman13]

Hello,

I ordered a new p/p tone pot. A shame that that last one only lasted a few months. I may have cooked it 🤷‍♂️.

I'm game to take the thing apart and see if I did fry it, is there any way to visually tell?

[reTrEaD]

Jan 1, 2024 0:15:30 GMT -5 bluesman13 said:

I'm game to take the thing apart and see if I did fry it, is there any way to visually tell?

From the symptoms you described, you no longer have continuity from the middle lug of your pot to the wiper. Your pot might be constructed a bit differently from the image below, but the concept will be the same.

On the right side of the image is an insulating wafer that has a carbon track that provided resistance between the two outer lugs. The middle lug is connected to a metal ring. The movable part that's attached to the shaft makes contact between the metal ring and the carbon track. There may be lubricant that has been cooked into a polymer that's preventing the movable assembly from making contact to the ring and/or the carbon track. Or the movable contact may have fatigued and lost it's spring tension, and there is a gap between the movable assembly and the ring and/or the carbon track.

[bluesman13]

Hi reTrEaD, Mike, sumgai, et al,

I've attached a pic of the disassembled pot. The pot is made has the number A250A stamped onto the ring of mini pot. The only thing I see that looks different is where the black ring terminates by the middlr lug, the left side is missing a piece of gold that outlines the ring (maybe that's nothing). 

Since that pot is only a few months old, (and worked fine prior to this installation), is it possible for the pot to short out if it touches the copper shielding on the inside of the control cavity? It's a telecaster so there isn't a lot of space - and, in order to make my life more complicated, I reversed the order of the pots so that the push/push pot is in the middle position instead of the end (closest to the bridge pickup). In order to fit in the tone pot in the middle space, I had to "dremel" out the control cavity where the tone pot goes and also the space where the selector switch sits. For some reason, Fender decided to leave a "hump" in the control cavity.

[reTrEaD]

The inner ring attached to the middle lug isn't supposed to look like that. It should be bright shiny metal. Instead it looks like a well-seasoned frying pan. Probably lubricant baked into a non-conductive polymer. Might have the same polymer baked on the surface of the carbon element.

Feel free to scrape the surfaces lightly just for S&G to see if you can re-establish continuity between them and the moveable contacts. But even if you do get continuity, bin it.

[bluesman13]

Just for fun, I tried to scrape the pot as best I could. I was able to establish a reading on my multimeter - CCW reads 364k and CW reads 1. As shown in the picture, I originally scraped the carbon coating thinking that that would increase the continuity - that may account for the >250k reading? Although, shouldn't the reading be 1 when the pot is all the way CCW and 250k at the way CW?

[bluesman13]

if a pot touches the shielding in the control cavity would that short out the pot or cause it to fail?

[reTrEaD]

Hi bluesman13

If the case or the bushing of the pot touches the shielding, that's no problem. If one of the lugs of the pot touches the shielding, it would short any signal on that lug to ground. But that's only a temporary problem. After making it so the lug stops touching the shieling, the short won't be there anymore and there won't be any damage to the pot.

[bluesman13]

thanks reTrEaD, appreciate your assistance!

[bluesman13]

I hope it's ok to ask another question using the same diagram. I wired up my tele using the diagram posted in the initial post. The only change I made was to replace the existing treble bleed with a .001uf capacitor and 150k resistor. The issue is that the guitar is way too trebly. In looking at the wiring diagram, I was wondering if changing the the .022uf cap that connects the lug on the tone pot to gnd and to the vol pot to a different value would make the guitar less trebly. I have tried using the tone knob and amp adjustments to try to ameliorate the situation to no avail. Thanks everyone.

[sumgai]

bm13,



This is easy - simply hook up a fixed resistor from the Volume pot's hot (incoming) side to ground. In most Fender guitars, the Volume pot is 250KΩ, I'll assume your's is too. So a good starting point is a fixed resistor of the same value, 250KΩ. But here's a trick: in order to get the right value, don't solder it in just yet. Instead, use a pair of alligator clips and some wire to bring that resistor outside of the control cavity. Now you can experiment with different values until you find the one that works best for you.  It may be higher or lower, be prepared to experiment for awhile.  (In the alternative, you can just use another pot, and when you reach the magic spot, measure it with your multimeter.  Fixed resistors can be found pretty close to your reading.)

I'm sure you know what to do after this, right?

HTH




sumgai

[bluesman13]

hello sumgai,

just want to make sure I understand - (we're not talking about a treble bleed, right?) - you're suggesting that I attach a resistor to the input lug of the vol pot? What changing the .022uf cap attached to the tone pot to a higher .033uf make the tone less trebly? thanks again for your assistance...Steve

[sumgai]

'master,


Well, time for some semi-serious schooling.

In short, if a pickup is not "loaded" (explanation in a moment), then it will sound out with all the treble it can possibly muster. Now a load is something that essentially 'resists' the pickup's efforts to produce all frequencies as loudly as it can. Your first encounter with a pickup-under-load is the two controls known as Volume and Tone - two pots present a load to the pickup, and the proof of this is that if you simply disconnect them, and run the pickup(s) straight to the amp, your tone will be more than a bit louder, and more than a bit treblier.

So it stands to reason that putting a resistance (those pots) in parallel with the signal from the pickup will result in less trebles, right? That "resistance in parallel" doesn't have to be a pot, nor is it necessarily limited to just one or two resistances - you can put as much, or as little, load on that pickup 'hot' line as you wish. You may have read other threads here where we warn some folks about having all four pots (i.e. a 2V2T setup like a Les Paul, etc.) in the circuit at the same time. We're calling that a 'pretty hefty load on the tone', aren't we.  Right about now, I'm sure you're putting two and two together and realizing that we're actually warning the modder about loss of tone, or more correctly, about loss of higher frequencies that are useful and in most cases, desirable.

Now in your case, you still have too much treble. So it now also stands to reason that by merely introducing even more "load" into the circuit, you're going to knock down some of that shrillness. All of which is to say; Yes, you've interpreted me correctly: put an additional resistance from the incoming side of the Vol pot to ground, and see what happens to your tone. In some cases (dare I say, most cases), you'll want a value much higher than the Vol pot's value, because of Ohm's Law - resistances divide in parallel, they don't increase in parallel. In other cases, a value equal or even lower than that of the Vol pot may be needed. Which is why I said "be prepared to experiment", and why I volunteered the "bring wires outside of the control cavity for easy testing" method. (And yes, I know you have a Tele and could just leave the control plate hanging loose in order to switch things around, that last bit is for other readers with Strats and such.)

Capice?

HTH





sumgai

[bluesman13]

thanks sumgai for the explanation and the suggestion! Steve