Odd behaviour from tone pot

[slidincharlie]

Hi,
I'm new here.

I have a problem with the neck tone pot in my guitar that is driving me crazy . Hope someone can help me.

The guitar:
my '66 Guild Starfire V, wired with the hot lead from the pickups going to the center lug of the volume pots, like stock. Link to the schematic

The problem:
the sound of the neck pup gets thinner and weaker (instead of getting darker) when I roll off the neck tone pot. This happens now with a new 300k tone pot as it happened with the old (500k?) pot.
This does not happen with the bridge pup.
The neck and the bridge pup/pots assemblies are identical.
The tone cap is a .022 orange drop.
The neck volume pot works beautifully.
I have tried a different wiring and two or three different caps to no avail.

Any advice is highly welcome...

--Carlo

[ArtieToo]

Thats truely odd. I know you've double-checked, but triple-check. Here's what to look for: What you are describing is what would happen if the tone control, somehow, got placed in series with the pups hot wire instead of in parallel. Look for a bad ground on the volume pot. Stuff like that.

I can't think what else to tell you to try.

[slidincharlie]

Thank you Artie.

An update:
the neck tone works normally when both pups are engaged. It works oddly as described only when the neck pickup alone is engaged... :-/

[ArtieToo]

Again, that would point to either the neck tone pot or neck volume pot missing its ground.

[slidincharlie]

Artie,
there is continuity (<1 ohm) between any ground point in any of the pickups and the bridge: all the pot backs are connected, and these are connected with the Bigsby bridge via the jack.

--Carlo

[slidincharlie]

A new update:
I've found that the neck pickup has got something wrong: it reads 0.L (open?) on my DMM.
It sounds apparently normal (maybe brighter than expected, but not weak); could this apparent internal problem be the cause of the odd behaviour of tone pot describd above?

--Carlo