FIXED Sharp Microwave R-930AW won't turn on

[J_R_E]

Model Number

R-930AW

Brand

Sharp

Age

More than 10 years

Older microwave but built-in and custom for space so would love to fix it. Won't turn on - nothing on the display when plugged in. I opened it up and tested the fuse and it was fine. Where do I go from here? Thanks!

 

[rickgburton]

There's two cabinet interlock switches where the power cord attaches. Make sure the white wire is connected to the power cord "N". The "L1" side of the power cord goes through one interlock and the "N" goes through the other interlock. Check for 120 VAC going into the switches and 120 VAC coming out of the switches. L1 goes to the board through the main fuse, the cavity TCO, and the mag tube TCO. It's relay 1 (RY1) COM (black wire) on the board and N is the white wire in CN-A connector pin #9.

 

[J_R_E]

Ok- I tested the three switches (interlock and monitor) for continuity and they seem fine. I confirmed 120V where the power cord attaches and between the main fuse (both sides) and the neutral at the board (I didn't see RY1 on the board - still looking). What can I do next? If I need to replace the board is it even available anymore?
Thank you.

 

[rickgburton]

I tested the three switches (interlock and monitor)

Those are the door switches, not the cabinet switches.

 

[J_R_E]

Ok - sorry, I'm new at this. I don't know what to look for then. I can see the switch above the turntable motor (which I tested and cleaned) but the power cord attachment area looks like the attached photos.

 

[J_R_E]

Those are the door switches, not the cabinet switches.

Could this be the problem? Are these bad?

 

[rickgburton]

Could this be the problem

Hard to say. Probably not as discoloring is common on many boards. We don't normally test the board components. Service techs don't rebuild the boards because there are no parts available and there are no board schematics available. We are just looking for the voltage in and the voltage out. (The resistors look like 18Ω if you want to check them). Here's a picture diagram. I traced L1 from the power cord to the RY1 on the board in red. There are several ways to check it.
1- Unplug the machine and check the components I marked A=case interlock, B=Fuse, C=Oven thermal cut-out, D=mag tube TCO, for continuity. Be sure to remove at least one wire from the component.
2- Machine powered. Meter set to measure VAC, insert one meter lead in the back of the connector of the white wire, CN-A Pin #9 and leave it there. Touch the other meter lead to the test spot marked 1. Your meter should indicate 120 VAC supply voltage. Touch test spot 2; 3; 4; 5; etc. etc. until you lose the 120 VAC.

I tried to make it as simple as possible for you:

 

[rickgburton]

If your meter leads are too big for the connector, try something like this:

 

[J_R_E]

This is perfect - thank you! Is this part the mag tube TCO? If so, I'm not getting continuity when I test it.

 

[J_R_E]

Scratch that - figured out it is the thermistor. Testing continues...

 

[J_R_E]

Ok - super confused. After testing a few components and plugging in the microwave to start tracing the 120v, it made a noise immediately upon being plugged in and I saw that the display was lit up. Sure enough, it seems to work now. Dirty contact that I cleaned just enough by unplugging/plugging in a lead? Also - I finally identified the thermal cut out location and tested it for continuity and there isn't any. This is after the microwave worked. I presume I replace it, put everything back together, and call it good? Thanks!

 

[rickgburton]

If it works, it works.