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Lost volume on my Fender P bass (photos which may/may not help!)


Walker
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Hoping someone can help with this.

I've lost volume on my P bass.

I  plugged in my Fender Road Worn P (which has a StewMac Golden Age Pre-wired Harness for P-Bass) yesterday and I had no volume. It's been working fine and has just been hanging on the wall, so nothing obvious has happened that could have caused this.

Signal is registering on my tuner, and if I crank the volume to max on the amp, I can just about hear some hear the notes among the hiss.

If I turn the volume down, I can't hear it (as expected), but if I turn the volume back up again and turn the tone down, I can't hear it either. With both pots to max, I can hear my plucking.

Tone pot reading 241k - 485k

Vol pot reading 0 - 241k

All wiring is solid with continuity as expected.

I'm at the very limit of my limited knowledge and I'm at a loss! Any idea why this could be?

Cheers

Chris

IMG_4624.JPG

IMG_4623.JPG

IMG_4622.JPG

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Assuming this to be a daft question but since in debugging NO questions are daft... it's not the amp, is it? I trust it's been checked with other guitaren?

Otherwise, the tuner doesn't have a microphone that could be hearing notes that way?

is something shorted to ground?

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Good questions! The tuner is in my Kemper, so through the cable, my other bass and guitars work fine, I've tried other cables and amps.

If something was shorting, could that affect the volume?

Is that tone pot reading what it should be? I'm not sure how the cap would affect the numbers on that pot (if at all)!

I'm cluless!

 

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That some signal at all reaches the amp means that you *have* a signal path, but something is 'attenuating' it, which is what the variable resistors do anyway, the couple the signal to ground through some magic bits of tat. that the signal is not GONE means there isn't a hard short to ground, but something like the dielectric breaking down in a cap or in the jack socket MIGHT create a resistive path to ground.

I'm new to this forum and I don't think anyone's twigged that I'm an idiot yet :/

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There are ways to test them but they're complicated and magic, mr carlson's lab on youtube goes into lots and lots of detail about 'how this stuff works' but you need a magic tester to test them properly and i don't even know anyone who has one of those.

If you had a wiring diagram you could try bypassing parts of the circuit to narrow down where the broken bit is, perhaps?

Here's something i don't know: can one connect a pickup directly to the output of the guitar? bypassing the volume and tone circuitry entirely, I can't think of any reason why not... that would allow us to see if we can get any life from it at all.

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Well I've never seen a more stupid way of fitting a cap.! If the long leg, earth side of that cap. ain't touching the 'unused' tag on the tone pot when fiited to the scratch plate, I don't know!

Should have gone to specsavers 

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It must be the volume pot... I'm getting continuity between the case and the middle tab :( and there is nothing attached to it except the white wire that I desoldered from the jack.

I've no idea how a high quality CTS pot could just go!?

I'll swap it out tomorrow once I've had a rummage in my parts box. Thanks again for the help. Really appreciated.

Enjoy the rest of Saturday night!

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in your second picture the top pin on the left hand pot (which is the one i think is the volume) is connected to the case of the pot (ground)

so you're measuring from the middle pin (wiper) through the resist out of that upper pin and through the case.

I *expect* that if you measure the value of that resistance and wiggle the pot, the value will change.

Enjoy your weekend too.

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Thanks for your help with this...

caitlin... I *expect* that if you measure the value of that resistance and wiggle the pot, the value will change. Yes, that's what's happening

Meddle... I've checked the points you kindly suggested and everything is clear.

Can I just check I've got this right and my extremely limited electronics knowledge isn't even worse than I thought!

If I do a continuity test from the case of the pot (ground) to the middle tab, there *should* be NO continuity, so I shouldn't hear a beep! In fact, if I do the same continuity test on any black to white wire on the harness, I shouldn't hear a beep. Is that correct?

That seems to be the case on my other bass, which I've just checked.

IMG_4623 copy.jpg

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pinching someone else's picture but i hope that's ok because they get their advert out of it:

WDUSS3L1101__24611.1481758669.jpg?c=2

you can see that if you trace from the body of the jack, up to the volume pot chassis, the right side pin is grounded that goes into the pot and connects to one end of the resist.

there's 'some distance of resist' before you reach the 'wiper' which is connected to the middle pin. you can then trace from the middle pin back down to the tip of the output jack... I think this is the resistance you're seeing.

We're dealing with AC current, not DC and 'leaking to ground' is what all these systems do deliberately to attenuate whatever frequencies they want to act on.

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Ah, I see, so I should expect to see a positive continuity test if i touch the two sides of the jack with my meter probes. I didn't know that.

It doesn't happen on my other bass, so does that mean a damaged component could be leaking too much?

Sorry if I'm being dull, but I'm finding this fascinating and trying to understand!

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20 hours ago, Walker said:

I've no idea how a high quality CTS pot could just go!?

There is "high quality" and a carbon track pot in the same sentence. Funny. You want quality, buy a conductive plastic or cermet track pot. Brands to look for: Bourns, Vishay...

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Just to answer the question above, you certainly can connect the pickup directly to the output jack - a quick and effective way to reassure yourself that the pickup is working. You can measure capacitors with suitable meter but to be accurate you would have to remove it from the circuit anyway (or at least one leg). I'd suggest wiring the pickup direct, if that works wire the vol pot, if that works add the tone pot. Hope you get it sorted.

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It was one of my pups. I eventually isolated and tested both and one of the was dead.

Beat's me how a pup can just 'go', unless it had a knock? Visibly it was fine, everything connected and decently soldered.

Oh well, £100 for new pups and £6 for a new pot I never needed. Up and running again.

Thanks for the help everyone :)

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A pup isn't much more than a coil of wire around a metal core, they fail the same way any winding does, either open or short. If the wire cracks anywhere along the length, electricity is gone from it. If it shorts *somewhere* then performance will suffer in weird ways.

You can of course rewind a pickup if you can be arsed and can count to quite high numbers or have a stepper motor you can employ :)

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