This is not a 'bug' in your XC12, but a sign that your XC12 is having belt problems. FF and PLAY do use the same technique, except for the fact that the PLAY is using the rubber-thing that pushes the tape down. (I have trouble explaining this in English)
Rewind is another technique, with is stronger in the XC12. So that works most of the time right.
When I test an XC12 I use a 90 minutes tape, and I try to Fast Forward this from the beginning to the end. When this goes real fast, and there are (almost) no slowing down parts in this process, I know the belts are fine.
When that fails: new belts are needed.
Good luck
Marius
p.s. try to use tapes from 30 minutes or less, they are not so 'heavy' for the mechanism.
Thankyou Marius1976 for your reply. I have looked at the belt and you are quite right it needs replacing, but the motor is not moving when I press play? only when I press rewind or fastforward?
I notice that on the XC12 diagram by Jerzy SOBOLA there is a Motor on signal from the SIO pin8? I am far from a electronics wizz how would I test this? I am at a loss
Regards
Zapp_man