B&O beocord 5000 model 4922, tray not open or close

I have just acquired this tape recorder, everything seems to work well after replacing the belts, but the tray doesn't open or close!
the tray and the motor move easily by hand, does anyone have any ideas what could be wrong?
the voltages supplying the motor appear correct and if i apply 9volt power direct to the motor it turns slowly.
have worked on electrical appliances for 40 years but never B&O products.