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This sounds like the control board for the CD player has failed, as its not completing its post check properly. That said it could equally be a faulty sensor which giving a false input into the control board.
The back and forth rotation of the CD is a clear sign of the control board not getting the require input.
Unfortunately the main board for this unit is now obsolete, so you will struggle to get a replacement, the best option is to get a donor unit with a working CD player, there is a similar model going on ebay for £10.
I just wanted to follow up and check if you required any further assistance?
I havent heard from you in a few days, and I just wanted to follow up and check if you required any further assistance?