If you can fast forward and rewind, then the belts are probably OK. Be advised that the computer controls the motor of the data recorder. If you just press the PLAY button and don't instruct the Atari computer to load/save data, nothing happens.
Try the following: Type CLOAD and press RETURN Computer Beeps Press the PLAY button on the data recorder Press the SPACE BAR key Now the cassette should start spinnning.
Press RESET key Press the STOP button on the data recorder.
To test more: 1. Insert a blank tape to the data recorder 2. Reset tape counter to 000 3. Fast forward until counter shows 020 4. Type 10 REM *** TEST *** and press RETURN 5. Type CSAVE and press RETURN 6. Computer Beeps Twice 7. Press PLAY and RECORD buttons on the data recorder 8. Press SPACE BAR key 9. Wait until READY is displayed 10. Press the STOP button on the data recorder.
10. Rewind the tape until counter shows 020 11. Type CLOAD and press RETURN 12. Computer beeps 13. Press PLAY button on the data recorder 14. Press SPACE BAR key
See what happens. If READY prompt is displayed and no error message, then your recorder is OK.
The number of Feebay listings you see whereby the gadger selling some Atari stuff usually says something along the lines of what Retrogamer was asking there, eg. "Got a light on the 1010/XC11/Phonemark but other than rewind it won't work...or the fast forward button's broken and I can't get it to PLAY so SOLD AS SPARES etc etc" - it does come across seemingly as though the data recorder is bust...
But as the chaps point out, this is indeed quite normal operation and if you look carefully at some of the LOADING instructions on most Atari game tapes, you should see something like this one on Scooter in the box out:
Hope the chaps have pointed you in the right direction there, RG.
The RETURN key is the key!
Definitely not a dumb question - we've all been there and pondered over similar unfathomables and then you either suddenly get the lightbulb moment - or you come to the lads on here who may well have been equally stumped at one stage - and now have it sussed through experience.