Hi,the problem with your device is a result of a weak assay(mechanical component),that's the reason why it runs for sometime and stops after a while,
The solution is to take out the device,and replace the assay which is attached to the pcb board,however the efficient and fast removal of the assay involves the use of a highly specialized equipment called the rework station,but if you are highly technical you can take apart the unit and remove the assay with the use of soldering kit and screwdrivers,however you have to be extra-ordinarily careful.

Thanks and take care

Hi,
hmmm...sounds like the transport motor/foot are stuck..open it up, and inspect around those items(where the tape actually clamps down) and see if you can see anything in there. Might even be a bug, no fooling..

The motor apply a different force when it does rewind/forward then when is in play mode. Also in play mode the tape is pulled from traction rubber wheel , not only by motor.

As posted check that motor is running in play mode when no tape is in. To do this locate and press the sensor pins inside deck, so that you can press play with no tape in.
alternatively put a cassette with no tape inside the deck, leaving deck door open (if the casset fit in with door open), or removing door.
If the motor does not spin main tractor when play is pushed, then probably it is a problem with mechanics, they do not start motor in play mode.
If the motor spin the tractors when tape is not in then it is the motor belt to be changed, it dilated and now does not have enough friction to move the tapes.

The problem is similar, check all the above with empty cassette, also press play and try to force for a little bit the tractor to run, the, the tractor may be stuck.
Additionally check that the rubber traction wheel that drives the tape is not stuck when you press play, if the wheel is stuck that is the cause for the problem..

Take care.