Without an inserted cassette and after pressing play the motor works fine.Likewise all the other functions Back/Forward and Pause also work. It is only with an inserted cassette when I press play or play/record that after about 20 or 30 seconds the head retreats and the machine switches itself off irrespective as to which part of the cassette is playing.
I have cleaned the heads and rollers
Thanks for your help

Rod I Gould, October 2006

there is probably a belt connected to the counter or reed switch which is a motion sensor, which tells the unit the tape is moving. if this belt gets worn then the machine thinks it has got to the tape end, and cuts off. you will need to open her up and observe /replace the belt.

romko, October 2006