20 year old Tappen microwave. Three door switches, one close to the hinge, two opposite the hinge. Had the cover off investigating another problem with door open.
Manually made one of the two opposite hinge (I’ll call top and bottom) and blew a 20A fuse in the microwave. With a meter on hot/nuetral I get the following with door open (so third one is always open).
Close Top/Bottom, 200 ohm
Open Top/Bottom, 200
Close only Top, 200
Close only Bottom, ANYwhere from 1 to 200 (1, 5, 10, 50, 80, 180, 200)
I thought I saw a pattern in how long I waited but it’s not consistent. It got me wondering if it’s some kind of fail safe (blow the fuse), like anti tie-down circuits in industrial controls.
Something tells me, and I could be wrong, that because of the inherent danger of running a microwave with the door removed (like it’ll give you deep muscle burns that you might not notice right wawy), it’s designed to short out if you try to bypass the door switch(es). I’d be willing to bet there’s another hidden one, perhaps a magnetic and hidden behind the case.
Doing some googling, there’s a failsafe switch, called an interlock monitor switch. I’m sure the exact name is different from model to model. It’s set up so that if one door switch is open and another is closed (ie broken) and the microwave is energized it blows the internal fuse.
If you’re monkeying around with individual door switches, that may be what’s happening.
Without the exact model number, I’ll leave finding out if this applies to your case and/or digging up and reading a schematic up to you.
I actually have a schematic from inside the cover and can see a short to ground. The range of the resistance is what puzzled me. I’m going to chalk it up to 20 year old switches that my DMM can’t read through consistently.
You might want to check the price on the switches before you put too much work into it. I don’t know why, but repairclinic lists some of those door switches as being over $50. If that’s the case, it might be worth replacing the whole thing.
Of course, they’re just microswitches, you can probably find a different one that’ll fit.