FUQ (eff -yu - cue) - FAQ's with an EDGE

Tagged As: Jackson Guitar Wiring Diagram

Question:
I bought a used Jackson Concert EX 4 string bass knowing it had a problem. That made it very affordable. Here is the problem; (pj pickups) and it seems the p works and so does the volume but no tone control, assuming even a poor product would have 'some' variation, and the J pickup does not work. Three knobs. The first most forward toward the neck I think is volume. It works The second or middle knob would seem to be the pickup control as there is a detent in the center of its rotation. Turned all the way counter-clockwise and nothing, no sound whatsoever. Just crack the knob clockwise and sound begins and gets fuller as you turn the knob more. The third and closest to the jack input has no effect on anything. Tone control I think. The center pot (pickup control) has what seems to be two pots stacked and the volume and tone have one each. I have no manual so my description of what the knobs control may be wrong. All the wires are attached.

Answer:
Sounds like you're right about the middle control being a balance between the pickups. One half of the stacked pots for each pickup. The stacked pots should work in opposite directions -- as one goes up, the other goes down. From what you've described, I'd guess that the problem is either with the pot for the J pickup or the J pickup itself (seems obvious). Ask the previous owner if the bass was like that ever since it was brand new, or if the problem suddenly developed. If it was like that right out of the box, then it's more likely that the problem is mis-wiring. If it happened later, then it's more likely that it's a component failure -- a pot or a pickup. You said you checked the wiring, but did you check it at the pickup too? Make sure the solder connections are solid all the way through the circuit, from the jack to the pickups. Contact Jackson for a wiring diagram, and follow the wiring to see if it's correct. If it is, then check the components -- swap the wires to the pickups, i.e., connect the P pickup to the wires the J pickup is presently connected to. If the problem is now reversed, and there is sound when you turn the balance pot full the other way, then you've determined that the J pickup is the problem. You could also check this by disconnecting the wires to the balance pots and connecting the wires from each pickup directly together (but not connecting the two pickups' wires to each other, keep them separate), taking the balance pots out of the circuit entirely. If the J pickup suddenly works, you know it's a pot problem. If it doesn't, then it's the pickup or the wires to the pickup. Keep your amp volume low, if you bypass the volume pots, you're going to go full volume from your instrument. Verify your results by doing the same thing with the P pickup, since you know that it works. Make sure you draw a diagram and mark your wires so you can re-connect them correctly when you're done. If you've got a VOM or other meter, test the balance pots by disconnecting all wires and then placing the probes on the terminals. Then turn the knob and watch the meter -- resistance should vary smoothly. If it doesn't, or if it stays dead, then your pot is no good. I suppose it's possible, too, that the pots are connected so that they both go full on at the same time, rather than one going off as the other goes on. That's a mechanical problem with the way the pot is built, so just replace it if that is the case. While you've got the meter out, check the pickups to see that there's continuity -- when you put the probes on the wires, you should get current through them. If not, you've got a bad pickup. Also, isolate the wires and check them for continuity, too. One may have been kinked or pinched, and is broken. You can replace the balance control with any balance control you find at Radio Shack or wherever -- try to match the resistance value as closely as you can, but it's not critical to get an exact match. Full on is full on, no matter what the resistance is when it's full off (full off might not be full off, though). Match it exactly if you can, but don't sweat it if all you can do is get close. They're not expensive, and if close turns out not to be close enough, then work harder and find an exact match. You could also try the brute-force approach -- just replace everything. Depending on how much you paid for the bass, your best bet might be to drop a brand-new set of Seymour-Duncans in, with new controls, and you end up with a bass that works right, and has better sound to boot. Sounds like this mystery could be fun to solve.