Help - weird electronics one

OK< this is a very odd one, need some help…

I had a Fender Vintera MIM P bass that I sold to a guy locally.
Original pickups, factory rounds put back on for him, everything worked fine.
He called me the other day to say something was wrong with it, it was ‘dead’, could he come have me take a look.

So he came today…and a few things were different from when I sold it

  1. He had put tapes on it
  2. He had a guy at GC do a setup
  3. He said he did some fiddling with it

Here is what I found.

  1. Put it on a tuner - had signal, able to tune, however, the lower strings appeared to be ‘cutting out’, but said ‘hey, I can tune it, try plugging it in and playing it’
  2. Hooked up to amp - very very low output, so, checked pickup height - which was huuuuugggeee - aha! - found the problem. Adjusted pickups
  3. Replay - overall, I feel like the output is lower than it should be, I couldn’t get my Berg’s clip light to come on with gain all the way up, but, could be played - EXCEPT - when you rolled the tone knob off all the way - then - could still hear it but almost silent. The string noise was louder than what was being amplified, tone knob back up - reasonable output and sound. HOWEVER - some very odd distortion on the E string. So, swapped out tone knob and capacitor, retuned, and…SAME ISSUE. As soon as you start to roll off the tone, volume gone!

My gut tells me there is something with the tapes he is using that is giving a much lower output to whatever stock P pickups Fender use on this thing, and when the highs are cut with the tone knob, there is not much left. I also think the E string distortion is because, with the tone knob up, the higher fundementals of the E is mostly what is being picked up or something.

He claims everything was ok with the tapes on then all of a sudden it wasn’t. I am not quite buying it.

I would assume tapes put out less magnetic field, and perhaps these pickups are kinda junky and not really suited for tapes, and the signal is just too low (high enough for the tuner to pick it up, but not high enough for proper amplification).

I then passed the signal through the B7K and upped the level quite a bit, played with tone rolled off but lots of background noise - I assume from all the gain adding.

My thinking is incompatible strings/pickups, even though he said they worked fine (for a while).


@Al1885 - ever run into this?

Hey @John_E , Did they replace any pots? maybe they put in 25k pots instead of 250k? Only other thing I can think of is a bad solder joint. You are a 5 star seller to help someone after they messed with an item after a sale.


Original pickups have defects?


He’s kind of a relied at this point so happy to help him.

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But then why are they “ok” with tone rolled up, or at least acceptable.

I’m thinking of throwing rounds on to prove or disprove my theory

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It’s interesting. Tapes have the same amount of metal moving through the field, just also a wrapping. I wonder if the tape interferes with grounding.

The strings when they vibrate disturb the magnetic field of the pick ups which is picked up by the woundings around the magnetic poles to produce a current. The bigger the disturbance the more current is produced which translates into what we call volume. The only way I can see the strings causing less volume is the metal content of the strings to be less than desirable. I have been reading about “fake strings” showing up on the market maybe this is what he got instead of what he thought he was getting. The packaging looks like the real thing in pictures but when you get the fake strings next to the real manufactures strings the differences are noticeable. The complaints I read about the fake strings are they work for a short while and then they don’t.

Swap strings now. This will either prove that the strings are the problem or eliminate them.

Man. I’ve never heard of “fake strings”, but nothing surprises me anymore (grumpy old man rant. “get off my lawn!”).

Swapped the E string with a good old round - no difference. Ugh.

I’m getting 5.3Kohms on each and a combo of 10.6kohms which is right where it should be. Ugh.

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I’ve got ground continuity and ~.3 ohms from bridge all the way to ground pickup connection.

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yeah but what about the strings

I would start testing the pots and see if they are still good.

My guess is that you have a bad capacitor.

Yep, thought that, too. A shitty cap will ruin your day, or at least your sound.

What is the value of the cap? And is the pot linear taper or logarithmic?

As stated above, I changed the cap and the pot, same thing! I’m stumped.

Swapped the E with a boomer, same issue.

.047 / 250 log - same as I use in every bass

What I don’t get is that the issue clearly is related to what is happening when the tone circuit is engaged, even a bit.

Wiring is exactly like this…

So, when the tone pot is rolled up, it is basically taking the cap out of the circuit - signal is louder, but, I have to say, not as loud as I would expect. I cannot get my amp to clip at any gain setting, which is uncommon. When the cap is engaged, almost zero signal, minimal.

This signal difference is even apparent using the ‘screw driver tapping the pole test’ - and VERY apparent.

So, since the pot and the cap swap, and the string swap did nothing - and the pickups are reading an appropriate resistance, I am now thinking something is ‘stunting’ the signal overall, which is in turn made worse when the cap is part of the circuit (less electrons, less flow across the plates, even less sound). Going to check the jack and the volume pot and all the other connections will get a resolder just for good measure.