Ibanez SR505 electrics issue - schematic?

[blindboybenton]

Hi
I don't do guitar repairs just stick to amps, But i was asked by the guys in the guitar shop
where my workshop is located

The bass went to a local store and was returned not repaired ( same fault)
It came in the shop here and i was asked if i could have a look at the pre amp
as a flavor

The fault is that the treble pot is acting like a volume control when you compare to the stock its clearly faulty


When compared to a SR505 bass off the wall the active circuit is just not the same lacking in punch/tonal adjustment , unfortunate that this bass has a different pre amp
They have checked the pots and battery all good
I had a look and tested what i could on the pre amp board all meters ok
checked values of resistors and checked if the smd caps are short
I decided to change the OP amp, this made no difference
The wiring is ok and correct as far we can see


I hooked up a signal gen to see if i can work it out what is going on. I work better with a diagram,
Replacing the active circuit is not an option due too the cost of parts and labour

If anyone has any info... thanks in advance

BBB