20 Most Recent Sharp R-520KS Microwave Oven Questions & Answers

You need to replace the control panel, the panel is all one piece buttons and all.

Most likely needs a new membrane switch. Part number FUNTKB445/KIT description "KEY SHEET", part is backordered, lists for $13.18. Find Sharp service centers here.

You can tell if microwaves are being emitted if you get warm standing in front of it (seriously). But I wouldn't recommend that unless you want to cook yourself.

First thing that comes to mind is the door interlocks are out of adjustment or bad. Home microwave ovens are not supposed to operate like that. Some commercial models start the fan right away and run it after the cooking cycle is completed but I've never heard of a consumer model that does that.

Find your closest servicer here and have them take a look.

Magnetron and accompanying high voltage diode are usually to blame. Everything else works but the magnetron isn't resonating (providing the proper energy to excite your water molecules).
An appliance repairman can change it for you (typically $180) or you can get a new microwave.

It should be an Omron D3V-16G-3C25, you can google that number and find a few electronic parts suppliers who sell them in a quantity of one. Likely the cheapest route is to buy off of eBay where I see them for $10 shipped.

Did you disconnect and test the three latch assembly microswitches with a multimeter or continuity tester? The top and bottom switch are normally-open, and the middle switch normally-closed. The lower switch seems to be the one that takes a beating and most often fails. It should be an Omron D3V-16G-3C25 and can be found on eBay for $10, or via an electronic parts supplier.

There are three microswitches in the door latch assembly. One of them has failed (most often the lower one). With some mechanical know-how one can easily replace the bad switch with just a phillips screwdriver. There are two normally-open switches, and one normally-closed switch. They can be purchased off of ebay for about $10, and changed in 15 minutes.

The fuse will be a 20amp ceramic. The fuse should be available at hardware stores, Radio Shack.
If the fuse is blown, there is a very good chance you have another problem, possibly a bad or misaligned door switch, shorted capacitor. Replace the fuse, if it blows again you will have to figure out why. Door switches are the most common reason for the fuse to blow.