How to Troubleshoot & Replace Lg AP4437957 / 3B73362F Microwave Door Switch

Replaced microwave door switch. 

Two screws, remove input module. Behind, you will find the micro switches top and bottom. Pull connectors and change out switches. Replace input module. 

We replaced it. It took a bit to find the bad egg. At first, we thought it was a bad diode, but after testing it, we found that wasn't the problem. We dug deeper after reading online and found a bad micro door switch. It was clearly blown. We called appliance parts pros, ordered the part quickly and it came in 2 days. It cost $6 plus shipping, and saved us >$250 to replace the whole microwave! 

A friend told me that was properly a switch that broke from opening and closing the door. Once I identified that I called your company, the gentleman that answer the phone from technical support was very helpful and ordered the switch he identified that I needed . Receive the switch and the unit is now working fine. 

Per your advice, I ordered a door switch, figuring that even if it didn't work, the part was inexpensive (shipping cost more than part!). Disassembled the front of the microwave as per a You tube video I saw and was surprised to see three switches, two identical to the one I purchased. Replaced the easy to remove top switch one first, started the microwave and once again, no heat. So I replaced the bottom switch (hard to remove) with the switch that I had just taken off the top. At first the microwave didn't work when I tried it while still partially disassembled, but after re-assembly, it worked like a charm. My next choice would have been the magnetron, which looked like a much more difficult project. 

I first took the top panel off to get access to the control panel screw. I then removed the control panel, took pictures of all the wiring and then disconnected it all. I then removed the holder locker, salvaging the middle door switch. I then installed the door switches on the new holder locker, added a new disconnect terminal to one of the wire pairs (it had gotten grease in it somehow and looked to have shorted at one point). Installed the new holder, connected the wires up and then wired up the panel and reinstalled. Plugged in the microwave, hoping that it would not catch on fire and then proceeded to testing. 

Very simple. Push down a tab. Pivot the switch. Slide it off the plastic post. Remove the electrical wire tabs. Reverse install. I located the bad switch noticing it's electrical connection was a darker color than to other one at the top. 

Replaced door switch. 

The belt was obvious. The microwave oven took some troubleshooting. Thanks to the schematic that was in a small envelope stuck to the frame I was able to check out all the electrical components. Found 2 bad door switches. Ordered them and replaced them. I saved a ton of money. 

Replaced the Humidity sensor, Thermistor and door switches. I replaced these thinking the problem was one of the items but didn't want to trial and error one part at a time. Plus the cost was reasonable so if these didn't help I wasn't out a lot of money. I sense the door switch was the problem. Replaced all items and the microwave works great. Thanks for the advice and the cost of the parts.