Could you help me fix some bass guitar electrics?

Question

I've tried to replicate the circuit as best I can here, I'm afraid it's more pictorial than scientific:
http://69.16.250.134/smarshonline/kingbob/wp-content/uploads/2012/01/basscircuit.pdf

I know a little bit about electronics, and a little bit about bass guitars, so my friend asked if I could fix his for him when it broke; the short answer is, I can't.

The guitar is a 4-string AXL Tiger Pro bass with 1 humbucker and 1 single-coil, 4 dials (not labelled) and a 9V battery socket (I guess that makes it an active bass?)

The manufacturer has gone bust or been sold or something; I did contact the current company with the same name, but their engineers were unable to help, or at least, so they said.

It might not be the world's best bass, but it means a lot to my friend and if you can help, please do.

My best guess is that the blue purple and yellow wires have come disconnected from the pot with no connections, but that doesn't explain the stray black wire, nor the strange solderings, nor does it tell me which terminal to reconnect them to. I don't want to do any damage to the electronics, so I won't do anything without solid advice.

Finally, if you can think of a better category to file this under, by all means include it at the end of your answer and I'll consider posting it there too; I figure engineers will know most about this, because the music section is more about listening to music, not maintaining instruments.

Many thanks,
Bob

GibsonEssGee · Accepted Answer

These kind of questions tend to turn up in Entertainment and Music under either Music or Other but Engineering is OK. The only information I've found on that particular model is that it is an "active bass" but I haven't even found a picture of one.

I've stared at this diagram and the purple/yellow etc. wires must go to a volume control pot.  Call me a bit thick but I don't see a stray black wire. One is the battery -ve and the other is the ground to the output jack (which doubles as an on/off switch for the battery). The B in the pot designation means a logarithmic taper. In all probability the missing volume pot will be log as well. I've had a rummage around trying to find a clearer schematic with no success and I am unable to find a datasheet on the preamp chip so I'm running on experience of guitar wiring here.

It's unclear if there are any connections to the B100KΩ pot on the right other than perhaps R7/C5. If they aren't connected to the pot then the blue/purple/yellow wire need to be attached to the pot with the purple wire attached to the middle connection of the pot, yellow to the top and the blue to the bottom connection. Fit a new battery before you test it. You should at least get some noises out of it then and take it from there if there is a still a problem although I suspect the new pot wiring should sort it.

? · Answer

Try connecting the purple wire to the lead under the letter B of the pot, the yellow wire to the center lead of the pot, and blue wire to the lump of solder. It appears that signal is being passed through the yellow wire to the pot and then to the purple wire before leaving the PCB board. If this doesn't work you might just short the purple and blue wires together.

? · Answer

That was not a circuit diagram. You  need to post the actual circuit diagram in order to get help here !
From that image, it was just a simple tone control circuit. Mostly those potentiometers got defective after years or months service. Change all of them. That is the best way to fix this board for someone like you without knowing electronic. But I also doubt you could replace those parts since it requires soldering.

tronary · Answer

take a look here for some help

http://www.1728.org/guitar.htm

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Could you help me fix some bass guitar electrics?

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