Help with Music Man StingRay 4 please

[sonolink]

A friend has brought me his bass that has almost no output and the sound is brittle. I've opened it and noticed a TL082 chip. Measuring voltages I get 9.5v between pin 4 and 8, but I get 4.5v between all the other pins and ground. This is without playing any sound.

This is wrong isn't it? Should I replace the TL082 or maybe I should check something more before to avoid frying another chip?

Thanks for your advice and help
Cheers
Sono

 

[fazer]

Could be wrong but 4.5 volts would be the bias voltage to run an opamp off a single supply of 9 volts.

 

[Newmarket]

Those voltages sound okay. The signal pins are biased at around the mid point of the voltage supply. That is correct.
I'd suspect the pots first.Doed giving them a good waggle alter anything ? Try bypassing the preamp if it's clear where the input(s) and output are.

 

[Newmarket]

*Does

 

[Ricardus]

So it has a preamp powered by 9v battery?

Do you have a schematic?

 

[sonolink]

Hi guys,
It was the volume pot!!!
Thanks for your input, time and help!!!

Cheers
Sono

 

[Newmarket]

Could be wrong but 4.5 volts would be the bias voltage to run an opamp off a single supply of 9 volts.

Spot on. Your reply wasn't here when I responded just after you posted. Yes - basically all kit running off a dingle supply needs to split the supply to give a reference voltage for the audio such that the audio signal remains within the voltage rails (with whatever headroom required). With op amp stuff this is usually an equal or near equal split. Discrete transistor stuff may be optimised at some other ratio but same idea.

 

[Newmarket]

Hi guys,
It was the volume pot!!!
Thanks for your input, time and help!!!

Cheers
Sono

Well sorted. Yes - pots wear out / get dirty and wiper contact can be one intermittent or just a capacitive coupling where you basically just get "hf crosstalk" to the output.
If the pot allows you can try squirting in bit of DeOxit and working the pot' before resorting to replacing the pot' if that is more convenient. I've had a lot of success with this on a guitar amp. Around 16 pots' that were useless and now good. A few took two or three applications.