I'd noticed that my cassette tapes were playing slowly so set about doing a bit of research. The drive belt on my unit was replaced not long ago and it didn't appear to be slipping. I'd read about adjusting the play speed via the potentiometer on the motor. I managed to find it and made an adjustment that has resulted in the tapes playing at the correct speed; always preferable.
After removing the unit and carefully bending the side tabs outwards, remove the bottom metal cover. Taking care not to touch or damage the internals, you should see the motor to the right. (see photos).
There is a small access hole on the motor that is covered by an equally small black rubber dust cover. (see photo). I used a small crosshead screwdriver and pushed through the dust cover, which has a crosshead design. (I disconnected the unit first, adjusted then reconnected to check). Turn clockwise to speed up and anticlockwise to slow down. Mine only needed a tiny adjustment and took a couple of attempts before I was happy.
