the turntable in my sharp microwave won't spin at all, just sits there.

Diagnosis

When the turntable on a Sharp SMC1585BS fails to rotate, the issue typically stems from one of three failure points: mechanical obstruction, a stripped drive coupling, or a complete electrical failure of the synchronous motor. Because this model uses a high-torque convection system, the turntable is subject to more vibration than a standard microwave, which can lead to the glass tray shifting slightly off its center axis, causing the roller ring to jam. If the tray is seated correctly but still won't move, the most likely culprit is the drive coupling (the plastic D-shaped piece that connects the motor shaft to the roller ring). Over time, the plastic teeth on this coupling can strip or crack due to the weight of heavy convection-ready cookware. To confirm a motor failure versus a mechanical jam, listen closely during operation; if you hear a faint humming or clicking sound coming from the bottom of the unit but the tray remains stationary, the motor is attempting to engage but the coupling has failed. If there is total silence and no movement, the motor's internal windings have likely burnt out.

How to Fix It

Follow these steps to isolate and repair the rotation assembly:

1. Power Isolation: Unplug the microwave from the wall outlet completely. Do not rely on the "Stop" button, as the capacitor inside the unit can hold a dangerous charge, but the motor area is generally safe once unplugged.
2. Tray Alignment Check: Remove the glass turntable tray and the plastic roller guide ring. Inspect the roller ring for any melted plastic or debris stuck in the wheels. Clean the floor of the microwave cavity with a damp cloth to remove any grease buildup that might be creating friction.
3. Coupling Inspection: Look at the center of the microwave floor. You will see a plastic drive coupling protruding from the base. Rotate it gently by hand. If it spins freely without resistance or feels "loose" on the shaft, the coupling is stripped.
4. Coupling Replacement: If the coupling is cracked, pull it straight up and off the motor shaft. Slide a new replacement coupling (ensure it is the exact part for the SMC series) onto the D-shaped shaft until it seats firmly.
5. Motor Replacement: If the coupling is intact but the motor is dead, you must remove the outer cabinet screws. Locate the turntable motor mounted to the underside of the chassis. Disconnect the two spade connectors from the motor terminals. Unscrew the motor mounting bracket, remove the failed motor, and install a new synchronous motor.
6. Reassembly: Reinstall the cabinet, place the roller guide ring back in the center, and set the glass tray specifically into the notches of the ring. Power on the unit and test with a light load.

If That Didn't Work

• Check the Roller Ring Track: Inspect the groove in the bottom of the microwave cavity. If a small piece of food or a plastic shard has fallen into the recessed track where the roller ring sits, it can create enough friction to stall the motor. Use a toothpick or a vacuum to clear the perimeter of the floor.
• Verify the Glass Tray Fit: Ensure you are using the original Sharp glass tray. Third-party replacement trays that are slightly too heavy or have a different center-hole diameter can put excessive axial load on the motor shaft, causing it to trip its internal thermal protector and stop spinning.
• Inspect the Wiring Harness: If you have already replaced the motor and it still won't spin, check the wiring harness connecting the motor to the main control board. Look for signs of rodent damage or charred wires near the convection heating elements, as the heat from the convection fan can sometimes degrade the insulation of the motor wires.
• Test the Control Board Relay: In rare cases, the relay on the main PCB that sends power to the turntable motor fails. If you have a multimeter, test for voltage at the motor terminals during a cycle. If no voltage is present, the control board requires repair or replacement.

Heads Up

• Weight Limits: Avoid placing extremely heavy pots (over 10 lbs) on the turntable during convection mode, as this puts immense strain on the plastic coupling and can strip the gears instantly.
• Cleaning the Ring: Regularly remove the roller guide ring and wash it with soap and water. Grease buildup on the wheels is the leading cause of "stuttering" rotation.
• Avoid Forcing: Never manually force the turntable to spin rapidly by hand while the unit is off, as this can bend the motor shaft and cause permanent misalignment.
• Safety Warning: Always disconnect power before removing the outer casing. Microwave capacitors can store lethal voltages even when unplugged; avoid touching the high-voltage transformer or capacitor area.