I Have a sharp microwave model # R1874. On the control panel, when I press the start button, the microwave runs for 59 seconds then stops. I have to press the start button again to have it run again. It seems to have set itself permanently to run only for 59 so if I press 5 minutes, it runs to 4:01 and stops. I press start again and it runs till 3:01 and stops until I hit start again. Help?

That would be a problem in the damper assembly, either a bad switch or motor, or the damper door is jammed or blocked. Consult the attached diagram for general reference. The damper switch is the same as the primary interlock (door) switch.



Its location varies by model, but you'll have to take the outer cover off to find it.

The best place to order Sharp parts is Tritronics or you can call them toll-free at 866-779-5835.

If you only need a switch, you can order a universal type HERE

Also, I quote other similar solution...
I had the same problem. Turned out to be the micro switch and damper motor. I replaced both myself and fixed the problem for less than $40.00. The best advice I got was replace the switch, reconnect the motor and make sure the motor runs through a damper door cycle. It didn't run, even though it showed continuity and had power, so I replaced the motor which solved the problem. The micro switch which is activated by the cam on the damper motor has to be cycled within one minute, or the unit shuts itself off. The damper motor on my model R-1870 is found in the right rear section of the assembly when facing it. You have to remove the unit, and remove the outer casing to get to it. The damper is a simple sheet metal door, activated by the motor, and the switch mounts at the top of the motor and is activated by the same cam that activates the door.


Good luck.