there may be a short somewhere in the feedback loop of IC301A.
I would check VR301 first.
refer to the datasheet of the pot for pin designations:http://www.mouser.com/catalog/specsheets/TW-700148.pdf
the distortion circuit using the first gang of the pot, pins 1, 2 & 3 (the ones without the circles around them in the datasheet).
First check that pins 1 & 2 are not shorted with solder.
If this is ok then lift one leg of R303 and test the resistance between pins 1 & 2 of VR301. The resistance should vary between 0 and ~1M ohms as you rotate the pot.
If everything is still ok you can rule out the pot as the problem.