How to Troubleshoot & Replace Ge AP3994062 / WB27X10928 Fuse

I ordered the capacitor, diode, and magnetron in hopes that I would be able to complete the repair using the less expensive parts. I first removed the oven from the wall and then I removed the metal housing to access the internal parts. I discharged the capacitor using a pair of insulated needle nose pliers. Then I changed out the diode and the capacitor and reassembled the unit and tested it. It still did not heat so I disassembled the unit again and replaced the magnetron this time. Reassembled the unit and tested it and this time it worked. With the excellent 365 day policy from Appliance Pro Parts you can return the unneeded parts. 

After purchasing the replacement bulb I had a lot of problem removing the cover.Turns out that three of the six screws in the back required a special tool. After trying different types of screw drivers to no avail, I took a picture of the screw and went to my local hardware store for some help. I had previously tried different sizes of Torx screw bits but none worked. It turns out that the screw was a Security Torx (has a center post in the middle of the screw) and required a TT20 bit, I was able to open the microwave cover and replace the lamp,by removing just two screws that held it in place and installing the new lamp in less than 5-minutes. I now have a security Torx bit set for toolbox for future use on other things. I almost threw in the towel and thought about calling in an appliance repair man due to the time spent (2 hours) going to several different hardware stores looking for the the right tool. 

GE Microwave/Convection Oven. Removed case (carefully). Tested in-line power cord fuse with multi-meter. Fuse was good. Noticed a scorch mark on a wire connected to the oven cavity thermal fuse. The fuse appeared to have been overheated from too much movement in it's mount. Removed part from unit and used number on the part to order a new one. Installed new part, re-assembled, and unit works fine. 

I researched the problem and found that not only was the fuse blown but the cause was a bad thermostat. Using the model number AppliancePartsPros.com. sold me the right parts for the right job. 

You-tubed "fixes." Ordered a fuse, diode and magnetron, in case it was any of the 3. Took apart the microwave as shown on video, found the fuse replacement, and wa-la, that's all it took. $6 part and I sent back the others for full refund. Saved me having to spend almost $400 on a replacement, and then another $125 for a trim kit. Well worth buying through AppliancePartsPros.com Will definitely do business with them again. 

Removed the outside cover. And yes-the two bottom screws on the back are pinned, security screws. If you don't have the tool (and don't want to go out to buy it) just use a small hack saw to cut a slot in it so you can remove it. The repair was complicated by the fact that the oven is cabinet-mounted. So, extra work was required removing the ducting and outside case. Make sure the cover locks back onto the front frame when done. There are overlapping edges that should interlock. You don't want extraneous microwaves leaking out. Also make sure ALL screws are back in their proper holes so everything is buttoned up. For the small cost I also replaced the fuse while I was in there as the old one was 10-yrs old. Bought that here as well. Why not do that while you are in there? 

Changed blown 20A fuse and thermal fuse. 

I had to order a small set of TT20 bits to get the security screws out of the back. I ordered them from an online retailer. Once the security screws have been removed and the Phillips screws, the cover can be lifted off and away. My cover was stuck in the front. I had to wiggle it to get it to break loose from the tongue and groove seam. I had ordered a Magnetron, a fuse, a HV Capacitor, and a Diode. It did not take that long to replace the parts. I figured if I was that committed to get into it I would replace all of the parts. It's back together and it heats like New???? I did not realize how noisy the Magnetron had become over time. Now it's quiet. For half the price of a new one, it's up and running like New! Go for it. 

Looked online for self help. Ordered Magnetron, Diode and fuse. Started with Magnetron. Took out old one after disassembling. Putting in new one was a bit of a problem, but eventually got it in. Hooked back up, and it worked. 

If you search for this issue online, you’ll see this is caused by a faulty door switch - the primary interlock micro switch (with the red button). This switch is at the lowest position in the bracket that holds the switches. The hardest part for me was pulling the cover off. Two screws on one side of the black cover, one on the other side and several screws in back. The cover slides back. The switches are clearly visible on the right hand side. The white door paddle presses on the switch button to actuate it. That paddle makes it a little difficult to extract the switch from its clips, but it will come out. The switch pops out sideways, not straight back like you might expect. The switch was replaced with ease, and voilá, problem solved. The oven works as it should.