488 mkii pitch control not working properly

[488 Recordings]

I bought a 488 mkii about 6 months ago. The door was missing, but I didn't mind that. The picture on ebay showed a the original pitch knob, the gray one with a white mark. Mine showed up with a shiny plastic one, without any mark. I drew one in with sharpie. Anyways, it only seems to work in the negative direction, but only for a few seconds before speeding back up to it's regular speed. It doesn't respond at all in the positive direction. The pitch control pcb seems to be intact, but I don't have a multimeter. Any ideas how I could fix it? I only know the basics about electronics, but I do know how to solder.