You can take out the turntable, and gently try to wiggle the little square-headed device (the coupler) that drives the turntable. If the coupler feels loose, it's probably broken.
If it feels tight, grip it very firmly with your fingers and try to turn a little it as if you were imitating the motor. If it turns the motor, you'll hear the whining sound made by the motor gears. That would mean your coupling is probably okay. It takes a little force to turn it.
If it doesn't turn, you may not be turning enough, or the coupler may be bad. You will probably need to remove the motor to check the coupling.
Sometimes the turntable support will warp / bend and no longer make contact with the turntable motor or coupler.
The way I fix this is to heat the support over a stove flame, then place a heavy weight on it so it holds the legs up in place a bit until it cools.
Here it is step by step:
1. Apply heat at points where each legs meet the hub (stove flame)
2. Place end of each leg on an object so that the bottom of the hub
is held up about 1/8" off the work surface.
3. Place heavy object on hub so the bottom touches the work surface.
4. Let it cool.
5. Test it.
6. If it still does not work, increase the height of objects in step two.
See: http://207.234.249.73/mwd/turntable_support_fix.gif
You can order parts for Sharp models from Tritronics at http://www.wehaveparts.com.
We have a similar service manual at our site which should help you be safe and do the job but note the part numbers are not going to be the same. See the Tritronics link above for parts.
The manual is at http://www.microwavedisplay.com/r1380_r1381_sm.pdf
William Miller † MicrowaveDisplay.com, March 2007
