sudden loss of output from j bass?

[tom skool]

hi all

My jazz has all of a sudden got very low output and the tone control has become an extra volume control.
Any Ideas?
I suspect a dodgy joint somewhere but I cant see anything obvious and I don't know my electronics enough to know where to look.
Its been wired in the master volume, blend, tone configuration as in the pic

Thanks

Edited August 12, 2014 by tom skool

[brensabre79]

Maybe something to do with the tone capacitor? It may be shorting. (green dot in your diagram)

check the legs of it aren't touching anything else, especially the leg connected to earth, or

remove it completely and see how you get on (you can always put it back)

[KiOgon]

[quote name='brensabre79' timestamp='1407929166' post='2525389']
Maybe something to do with the tone capacitor? It may be shorting. (green dot in your diagram)

check the legs of it aren't touching anything else, especially the leg connected to earth, or

remove it completely and see how you get on (you can always put it back)
[/quote]
This ^ but I'd suspect the other leg of the cap shorting to earth, maybe to the shielding?

Edited August 13, 2014 by KiOgon

[tom skool]

ok thanks i'll have a look. Might the tone cap itself have failed?
I did the wiring a year ago, it seems odd to me that it might now suddenly start shorting

cheers

[brensabre79]

[quote name='KiOgon' timestamp='1407929551' post='2525398']
This ^ but I'd suspect the other leg of the cap shorting to earth, maybe to the shielding?
[/quote]
Good point KiOgon, it could be either

And yes, sometimes capacitors do fail, although it may just have moved to be shorting.

[tom skool]

aaaaarrrrrgggh!

I couldn't see anything wrong anywhere so I rewired the lot. It made no difference! I suspected the cap so I swapped that, and I've checked the pups have their usual resistance.

This is doing my head in

[brensabre79]

DId you try it without a tone cap at all?

If the pickups are OK it's got to be something in the wiring. A short somewhere perhaps?

I'm afriad it may a case of trying to eliminate the rogue wire/component. If removing the tone control altogether made no difference it's going to be a process of elimination.

Starting with one pickup wired straight to the jack socket (you don't have to solder to check the signal - just touch the wires), introduce the volume control. If thats ok introduce the blend control. If thats OK add the second pickup to the blend (again try this direct first) etc. etc. At some point something will cause the drop in level... Last thing is to bring in the shielding one wire at a time...

Basically rebuilding the circuit from scratch you'll find the fault...

[tom skool]

Thanks that was usefull method.2days,3 complete rewires 3 dodgy volume pots later and finally i a have a working bass again, just in time for tonights rehearsal.
Thanks again all

[brensabre79]

Well done tom, next time it'll be much easier ;-)

[MoonBassAlpha]

3 dodgy volume pots?!! That's really quite unlucky, or you were doing something to damage or overheat them in the process of changing them. Well done for fixing it though!