(Another boring) wiring problem/question

[JVG]

I realise that wiring questions pop up fairly regularly on this forum, and aren’t the most exciting thing to read - please forgive me! I hoping someone with a keenness for trouble-shooting can help.

I’m returning my (lefty) Cobain Jag to stock configuration, in anticipation of selling it.

The problem: i’m getting no sound while in the bridge position of the toggle switch. The middle position is fine, so I’m definitely getting a signal from the bridge pickup to the switch. (The neck position, and the rhythm circuit, are both also fine).

My first thought was that the toggle switch had developed a fault, so i replaced it. That didn’t help!

I’ve checked my solder connections, and verified the signal path against the Official diagram but can’t identify the issue. 🤯

Ideas or suggestions welcomed, please!

[timtam]

The problem: i’m getting no sound while in the bridge position of the toggle switch. The middle position is fine, so I’m definitely getting a signal from the bridge pickup to the switch. (The neck position, and the rhythm circuit, are both also fine).

Since you are getting the bridge pickup in the middle position - just not in the bridge pickup position - and swapping to a new switch didn't fix the problem, there's a very narrow set of unusual possibilities: wrong type of switch, two bad switches, two switches shorting out only the bridge terminal when selected on its own, or somehow wired in a way that selects the bridge pickup in the middle position but not the bridge position.

What type of switch are you using ? Have you verified that the (disconnected) switch actually connects the terminal to which you have soldered the bridge pickup to the switch output, in the bridge-selected position ? And does not connect it to ground in that position ? Any difference when the switch plate is not screwed to the guitar ? A picture of the wired switch would help.

[JVG]

What type of switch are you using ? Have you verified that the (disconnected) switch actually connects the terminal to which you have soldered the bridge pickup to the switch output, in the bridge-selected position ? And does not connect it to ground in that position ? Any difference when the switch plate is not screwed to the guitar ? A picture of the wired switch would help.

Thanks for the ideas.

When I get a chance I’ll check that it isn’t somehow connecting to ground when in the bridge position, as you suggested.

I did unscrew the switch plate and gently manipulated the connections (while plugged in) to see if i could find a spot where it connected, but no luck there.

It’s a Switchcraft ‘short’ toggle, and appears to be in good shape, ie no visual distortion or damaged parts. The previous switch was the original unbranded short toggle.

While writing this it occurred to me that swapping the bridge and neck wires to the toggle could be a useful test, to see if the problem stays with the bridge pickup, or transfers to the neck.

[madlovepickups]

Are you 100% sure the bridge pickup is working in middle position? Try touching the pickup poles with something steel to make sure.

[JVG]

Are you 100% sure the bridge pickup is working in middle position? Try touching the pickup poles with something steel to make sure.

Yep, did the old screwdriver tap test. That’s why it has me so baffled!

Pretty busy with work for a few days, but will check it out again on the weekend.

[JVG]

Still can’t figure this out, but have tested a couple of things.

I swapped the bridge and neck pickup connections on the toggle switch, and this resulted in the problem transferring to the other side of the switch, ie the bridge position of the toggle worked (although connected to the neck pickup).

Therefore I am confident that the switch itself is mechanically fine.

I double-checked the middle position of the toggle, and everything is as expected, ie the bridge pickup comes through loud and strong. I did the screwdriver ‘tap test’ on the pole pieces to make sure i wasn’t imagining this.

The weird thing was that, when I disconnected the neck pickup from the toggle switch while in middle position, the bridge signal cut out too. In other words, the bridge pickup signal is somehow dependant on the neck pickup being connected. How can this be?

Is it possible the diagram is wrong? Can anyone with a keen eye see any issues with the bridge pickup signal path on that? (Link in initial post).

[timtam]

Schematics tell you if a circuit is capable of doing what it claims to do. My above schematic was drawn by tracing the official Fender wiring diagram in the service manual (same as your original link - Rev A, Jan 13, 2014). That schematic shows a circuit that clearly does what the switching matrix table says it should (that table also taken from the service manual). Ergo Fender's wiring diagram in that PDF would seem to be correct.

The fact that reversing the pickup connections to the switch transferred the same original problem that afflicted the bridge pickup selection to the neck pickup selection further suggests that the problem can only be something to do with the switch. It can't be the pickup or V1, or the problem would not have transferred to the neck pickup. In the lead circuit prior to the switch, the only thing that the two pickup circuits share is ground.

I realize this isn't your first rodeo, but it would still be good to see a picture of your switch wiring.

[JVG]

Thanks for taking the time to assist - i do appreciate it. My knowledge of electronics is patchy.

It’s hard to get a good picture, but hopefully these help.

The wiring may be obvious, but to be clear:

Red cloth wire is bridge pickup (via volume pot) and yellow pvc wire is neck (not actually attached in this picture, as i unsoldered it while trying to troubleshoot)

The black wires are grounds.

The yellow cloth wire sends the toggle output through a capacitor (not actually part of the original Cobain wiring).

[timtam]

The switch wiring looks OK from what I can see. You could cut off the protruding wire ends to reduce the chance of shorts, and the insulation stops a little short of the tabs (leaving exposed bare wire), but none of that is particularly unusual for Fender-style wiring. And that bare wire is probably unlikely to be explaining your issue if the issue if still there when the switch plate is out of the guitar (in that case bare wire can't be shorting to something in the cavity).


If you're returning this Cobain jag to stock, I would probably take the added strangle switch downstream of the switch out of circuit (or if not, at least until you get things working).

In order for the bridge pickup to work when selected, its hot has to get to the lead/rhythm switch. So you would put one multimeter probe on the switch tab there and the other probe on the middle tab of the VOL1 pot that the hot comes off before the toggle. You should have continuity when the toggle is switched to the bridge. To complete the pickup's circuit, you also need continuity of ground from the HB's green wire on the back of VOL1 to the output jack rim (where ground enters the guitar) - so test continuity between those two points too. The third possibility for no output from the bridge when selected would be a short between its hot and ground. So test between the VOL1 top tab and the green wire on the back of VOL1. You should not have continuity between those twp points when the bridge is selected on the toggle - you should see the full DCR of the bridge DiMarzio Super Distortion, around 14 kOhms.

If those all test out OK then the bridge pickup signal can be traced further.

[madlovepickups]

Could just be photo perspective but the switch ground terminal wires look to be awfully close to the red wire terminal. Definitely clean up protruding wire ends with some snips.

[madlovepickups]

Also the yellow pvc wire has some burnt insulation that may be exposing wires to the switch body?

[JVG]

Thanks again.

Agree the soldering is a bit crappy in these pics because i pulled everything apart and re-connected quickly to check things. Normally i am much neater, and would clip the protruding bits etc. i’ve checked that these aren’t causing the problem. I think the angle of the pics makes it look a bit worse!

I’m pretty much at the point where i think i will pull it all apart (wiring-wise) and start again.