A tired belt may not be your exact cause, but I've solved the wow problem before by simply using a slightly tighter/new belt.  Consider also removing the platter and check for anything which may be rubbing against the pulley - wires, gears, etc.  If you remove the belt and spin the platter clockwise it should spin freely without any rubbing noise for a considerable length of time. If none of that works, I'd imagine that you'll have to start looking at the PCB voltages. There are probably others more seasoned than myself who can advise.

I just changed the belt on my (mechanically very similar) BG6500 the other day and was reminded how much larger an old belt will be versus the new one (from DKSoundParts.) Putting the old belt on a flat surface showed it had not stretched evenly but rather around the area which had been in contact with the motor. (Doubtless due to a few years where it was packed in storage and not used.) Anyway, a new belt for the platter would be my first move. And on this model I can also reccomend cleaning off the old grease from the two metal rails and replacing with new TS-005 from DSP.

Thanks to all for the response, I'll order a new belt and grease for the rails.    

And check the subchassis riding height. A 12" record is larger than the platter, so will scrape on the surrounding surface if riding too low. It should have a 1-1½mm clearance with the carriage pushed all the way to the left. Note that the weight of the carriage shifts the subchassis' balance as it moves sideways. This will often cause wow/flutter and/or a scraping sound at the inner tracks of a record. Martin

Thanks Martin. I was trying to raise up the platter so it rotated free when an LP was on, and I wasn't getting it even all around, so started tightening (turning clockwise) the right hand screw, but now have a new problem that the platter is pulled to the left dramatically. Any idea of what I'm doing wrong? Or how to fix so I have even level and everything centered? Paul  

I managed to resolve the height and centering issue on the platter. I adjusted the speed pots to see if it would make a difference to the speed, but it only got up to 31.9 RPM, so I'll have to wait until I get the replacement belts in before i do any more with the speed pots. Thanks