About 3 months ago, on a Sunday, we had a sudden POWER off-on-off-on-off-on-off situation. A couple of hours later, after the electric company got us going again, I tried to heat up a bowl of rice in the microwave. It came on as usual, then after 3 or 4 seconds it hummed very loudly for a second, and then went out. It was completely dead. It turned out that the fuse was blown. I replaced the fuse, plugged it back in and the display lit up. When I turned it on to cook, the fuse burnt out again. I replaced it again, and fuse blew again. I removed the cover from the unit, discharged the capacitor and then removed the diode. I tested the diode with the diode test setting on my digital multimeter and it showed that the diode was open, (burnt out). I can find the diode online easy enough, but the problem I am having is testing the T.C.O.'s. The tco on the magnetron tested good (for continuity), the tco fastened into the bottom of the microwave tested good, (as a matter of fact they call it the bottom tco in the schematic. The black main power wire goes to it. I tested another one fastened into the bottom mounted next to it, and it tested open (infinity). On the schematic it was called the hood tco. I do not even know where the cavity tco is. Are these test readings incorrect, or should some of these test open? And where is the cavity tco? Also, is there a way to test a magnetron? This unit cost about $500 about 5 years ago. I know they are a little less expensive now, but I hate to buy a new, if I can fix this one. I had to mount it above the oven and customize a new hole for the vent.