Sharp microwave R-420LK does not power up

[ocn]

Model Number

R-420LK

Brand

Sharp

Age

6-10 years

The Sharp R-420 LK microwave we use in a toy hauler has suddenly stopped working. No signs of power. I've verified the outlet has power, moved into shop to bench test things. Fuse is fine. Capacitor seems to test out as OK. Door switch appears to be working properly. What should I test next?

 

[Dan O.]

There should be a couple of thermal fuses. Either of which if opened could stop all functioning. I haven't seen these particular types before but they should be able to be tested for continuity to see if they're defective.

Cavity Thermal Fuse

QFS-TA014WRE0 Sharp Temperature Fuse 150C

encompass.com

Magnetron Thermal Fuse

QFS-TA013WRE0 Sharp Temperature Fuse 150?C

encompass.com

Dan O.

 

[ocn]

Dan O. I found 1 fuse like those you posted it has continuity, so I'd guess is it ok. The traditional round tube fuse also checks out OK. On the circuit board there are 2 of these and when checked with an ohm meter they do not have continuity. But I have no idea if they should.
I

 

[ocn]

Upon closer inspection I see that the item on the circuit board is actually a relay of some sort, so it might be normally an open circuit with no power.

 

[Dan O.]

I have no idea how to test any of the components of the circuit board. If the board was found to be defective, the whole board would usually just be replaced.

Someone will have to look at the unit's wiring diagram to determine other possibilities. Most failures would not stop the control from lighting up, just heating or fan functions, etc..


Dan O.