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Not heating, everything works but at reduced power, fan and lights dim

My microwave won't heat but seems to be running at reduced power otherwise, the fans are quiet and the panel's dim, what could cause this?

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Hi @enotch3 ,

What is the make and model number of the microwave?

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Kenmore Elite 721.80823500

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Hi @enotch3 ,

A dim display and no heating etc may be due to low supply voltage.

Check if the AC supply voltage is OK to the oven and if so, check if the voltage is OK at the LV transformer connection on the control board.

If low there is may be a faulty line noise filter (part #5041Interior parts 2 Diagram

If the voltage supply is OK, here’s a link to the wiring diagram for the oven. (scroll to the right through the parts diagrams to find the wiring diagram)

There is a LV transformer (low voltage) on the control board that supplies the power for the board. The control board then operates the appropriate relays on the board to connect the line voltage for the motors, fans, HV power circuit for magnetron etc. to operate.

Long story short, you may have to check the control board for any obvious damage e.g. burnt out components, blown or bulging capacitors etc and also that there is the correct output voltage from the LV transformer. There isn’t any information regarding the control board so it will be difficult to find the problem unless there is something obvious to be seen.

Be safety aware when working with supply voltage and also in a microwave oven.

The HV capacitor in a microwave, can store >5000V DC for months even if the power to the oven has been disconnected for this length of time. This amount of voltage can seriously injure you. You need to correctly discharge the HV capacitor as soon as possible after removing the cover from the oven and before commencing any other work in the oven. If you don’t know what you’re doing then don’t do it!

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This could be caused by a problem with the high voltage diode, which helps to power the magnetron.

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