beocord 8002

I made following experience with my beocord: when I remove the belt from the pulley everything works fine, set time, Start time,stop time etc. Of course the tape is not moving. When I put on the belt everything works fine.However when I hit the play key the display goes to standby after 4 sec and the keypanel does not react anymore. The cassette keeps moving and the music playing. The beocord can then only be stopped by pulling the netplug. Anybody with ans idea why?

Could it be a connection issue by where the display and processor board hinge? I chased a couple weird problem that only happened when mine was closed.