Repaired my microwave today

[Lo_volt]

A few months ago, my microwave started tripping the circuit breaker whenever anyone pulled the door open while the magnetron was running. It never happened when we paused or stopped cooking before opening the door. Yesterday, my daughter pulled the door open in that specific manner and the microwave stopped working altogether. I checked the breaker and it wasn't tripped. It seemed the microwave was bricked.

Today I had the opportunity to open it and I found that the internal fuse was blown. The unit had a service pamphlet tucked inside so i pulled it out and looked it over. There was a whole section about a "monitor switch". I had to google what that was and interestingly enough, its function is to blow the fuse if it is still closed while the magnetron is energized i.e. door open and magnetron on. Being a 20 amp fuse it was a toss up whether the internal fuse blew or the house circuit breaker tripped. Finally, yesterday, the internal fuse bit the dust.

In poking around inside, I found that the monitor switch was very loose in its mount. A layer of tape tightened it up. Apparently the loose switch was still closed while the door interlock switches said the door was open and magnetron running. The tape tightened the switch in its mount and fixed the issue.

I guess this post is a heads up that GE microwaves have a monitor switch.

It's also a bit of a complaint that there's no indication of that specific fault. Those who are less technically inclined would likely have tossed the unit and bought a new one. This despite the possibility of a cheap fix.

 

[Diver300]

Microwave ovens have had switches like that for a long time, at least 40 years.

The switch is there in case other switches fail with the contacts closed for any reason. It is not designed to be used lots of times and you should get a new switch. You should check that the power to the magnetron is being shorted when the door is open. You can check that with a multimeter if you measure in the right place.

 

[camerart]

Hi,
A note for anyone with lower skill levels: Microwaves themselves are dangerous.
C

 

[Lo_volt]

Indeed, i pulled the switch and checked its function. Had it been sticky or seemed otherwise flaky I would have replaced it. It snaps into place so it has to have some slop. In my situation there was just a fraction of a second where the two door switches were in the closed state and the monitor switch was in the open state.

I knew microwaves had doubled up door switches but I did not know about the monitor switch. I can appreciate the redundancy as you really, really want to avoid a door open and magnetron on situation.

 

[Nigel Goodwin]

Indeed, i pulled the switch and checked its function. Had it been sticky or seemed otherwise flaky I would have replaced it. It snaps into place so it has to have some slop. In my situation there was just a fraction of a second where the two door switches were in the closed state and the monitor switch was in the open state.

I knew microwaves had doubled up door switches but I did not know about the monitor switch. I can appreciate the redundancy as you really, really want to avoid a door open and magnetron on situation.

It's what's known as a 'crowbar' circuit - a last ditch safety feature. Basically two of the door switches turn it OFF - if they should fail, the monitor switch blows the fuse to make it safe.

As an ex-microwave oven engineer I would suggest it's good idea to replace at the monitor switch if it's been triggered - needless to say a microswitch directly across the mains takes a lot of stress.

As others have mentioned, microwave ovens are EXTREMELY dangerous, the voltages and currents involved WILL kill you - in the UK you would probably struggle buying a replacement fuse, as no authorised service facility is allowed to sell you one.