Contactless testing by measuring magnetic field
Here I will tell you how you can check the operation of the Panasonic HV inverter on a safe and easy way.
If the microwave oven doesn't work, either the microwave tube itself or the HV inverter is defect. The first test is whether the microwave tube works, here you can see that it produces light:
Than, the HV inverter has to be checked. The high voltage on the circuit board is very dangerous and therefore it is safer not to carry out measurements on the circuit board itself, if it is not strictly necessary. See here how to do it:
Make a wire loop around the transformer core and connect a diode 1N4007 and resistor of 10Ω / 1W in series. If the HV inverter works well, the voltage should be:
- 1.6V with the microwave tube connected.
- 1.9V with the microwave tube disconnected.
You can also use an oscilloscope; the signals are identical with a disconnected and connected microwave:
Extreme danger if the HV PSU is not grounded
The high voltage power supply must always be grounded to the chassis ground with the ground cable. If not, it may expose the user to 4000V and cause extreme DANGER!
See the Microwave oven repair safety precautions and the Panasonic safety repair rules.
Automatic high voltage capacitor safety discharge resistor
After power off, a high voltage resistance of 100MOhm discharges the 3000V capacitors, which are (in my case) 5.6nF and 4.3nF. The RC time is 0.3s, so the high voltage is disappeared after 1 s.
