Microwave repair, not mine, commercial model. Worth about $1000 brand new with taxes included. Disappointing flimsy construction. Very little information available.
Fuse was blowing RANDOMLY only when CLOSING the door. I used up 3 fuses before I figured out what the issue appears to be.
The manufacturer suggested repair was to replace the door switches, a now obsolete relay on the PCB, and the fuse🙄 (there is a decal on top of the microwave, beneath the outer metal cover, listing the parts to replace if the fuse blows when opening/closing the door). But why replace switches or anything else until you can verify that something has failed or is at least not operating consistently? After testing the switches numerous times in numerous ways there was no reason to replace them - they worked!
Looked at the sequence of operation for the switches and door alignment. Door was a little wiggly when I first got it. Maybe enough that occasionally the sequence of operation for the 3 switches was disrupted? These were not quick determinations. Research was done beforehand about how microwave Interlock and Monitor switches are supposed to work in a specific sequence (no service manual could be found so I used general information from others manufacturer's service manuals to help). Then a lot of time observing how this model's switches appeared to be working.
Tested and observed the door closing as slowly as I could and watched the switches operate while listening for the "clicks". As well, connected DMM's to each switch set to continuity but preferred using an analog meter because it gave a better visual for the response time. Then I adjusted the door latch tightness with the door closed. Left about a 1/32" gap.
I have been testing the microwave all day, running it at different settings, opening and closing the door, checking that it is heating (dish of water), and it keeps working!
Cost = $18.00 for 5 fuses
(I'm not the cheap b*st*rd in this case. The guy who will be paying me is.)