On any model other than D followed by two digit models this problem is caused
in 90% of cases by the mechanism not returning to its fully stopped position
properly after carrying out and operation, thereby not activating the
appropriate sensor.
The thumping operation jolts the mechanism into the proper position whereby
the sensor can send the signal to the mechanism that all is normal, as
beforehand the logic circuits acted as though the mechanism had jammed whilst
conducting various operations, like loading or unloading etc.
Sometimes (only sometimes) even just pressing slightly on the cassette
door can correct the fault.
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