Toyota MR2 cd player keeps ejecting CD's

Question

I regularly read of other similar problems but have not seen a solution yet..
The unit is old (1991 ish),the radio part of the double DIN unit works well.
Every time a CD is inserted it remains for a few seconds and then ejects
Does anybody know if this is an alignment problem or a component failure?
I have dismantled the unit (very carefully) cleaned the laser lens (very carefully) and put the unit back together with no change in performance.
I realise I can buy an alternative cheaply but I really don't like being beaten
Anybody recognise this failure mechanism????