After researching the internet to see what would be the cause of the microwave working perfectly except that it did not heat up anything. I was told to replace the thermal fuse, so we bought and replaced both #17 & #18 fuses on the schematic, reconnected it, and it still will not heat up. What else could be the problem?
Answer Hello Debb,
This can be any of the high voltage components or the relay on the control board. These parts would include the high voltage transformer, the magnetron, the high voltage capacitor, the high voltage diode, or the electronic control. It could not be the thermal fuse since it would prevent the unit from running at all. You need to test in this order: Measure the resistance of the H.V. transformer. It should read as follows: Primary winding ......less than 1.0O. Filament winding ....less than 1.0O. Secondary winding approximately 50O to 120O. Measure resistance of the terminals on the high voltage transformer with meter on high scale.Primary winding to ground ....... Infinite ohms
Filament winding to ground ..... Infinite ohms
Now test the H.V. capacitor. 1. Disconnect power to oven and remove control panel. 2. Discharge high voltage capacitor. 3. Disconnect wire leads to high voltage capacitor. 4. Measure resistance of capacitor from terminal to terminal.
Normal reading—momentarily indicates several ohms and then gradually returns to infinite ohms.
Abnormal reading—Indicates continuity or infinite ohms. 5. Measure resistance of capacitor from terminal to case.
Normal reading—Indicates infinite ohms Abnormal reading—Indicates continuity.
Now test the diode. 1. Disconnect power to oven and remove control panel. 2. Discharge high voltage capacitor. 3. Disconnect wire leads to high voltage diode. 4. Measure resistance of diode in forward bias.
Normal reading—Indicates continuity
Abnormal reading—Indicates infinite ohms
5. Measure resistance of diode in reverse bias.
Normal reading—Indicates infinite ohms
Abnormal reading—Indicates continuity
If the diode tests good, replace the magnetron.