Among the most harmful electronic appliances to work with is the microwave oven. Thus, before performing any testing and troubleshooting, as well as repairs, you have to review some safety precautions to ensure your safety. The main rule in testing a high voltage capacitor in a microwave oven is to unplug it. Microwave ovens with high voltage capacitors work with a high voltage diode. This means that the capacitor can release a very dangerous electrical charge after the unplugging of the microwave oven.
Thus, always make sure that the microwave is unplugged and the capacitor is discharged. Remember that a high voltage capacitor can be discharged through a direct connection or short circuit. Here are the ways of fully discharging a high voltage capacitor:
- Touch the blade of a screwdriver (use an insulated screw) to the other terminal. Slide it towards the other terminal. Make sure that it connects or makes contact with the other terminal. Once the connection is done, hold it for about four to five seconds. If you see a spark, it means that the capacitor you are working with holds a charge and it is not defective.
- Do step one once again to create a short circuit with the capacitors as well as the chassis ground.
- Make sure that you create short circuits with each terminal. Thus, if the capacitor has three terminals, you have to repeat the first procedure with all the terminals.
- You may also apply a ground with the magnetron terminal to create a short circuit.
Now that the capacitor is discharged, here are the ways in which you may test a high voltage capacitor like the tantalum capacitor in a microwave oven:
- Make sure that there is no electricity running, so unplug the microwave oven chip cooler.
- To ensure your safety, double check the high voltage electrolytic capacitors. Make sure that they are all fully discharged.
- Recheck all the wiring of the microwave oven. Now, you may remove all capacitor leads. Perform this step very carefully.
- If you see a bleeder resistor, do not mind it. Do not remove it.
- Check on the ohmmeter for the resistance of that bleeder resistor.
- Now, measure the infinity of one terminal to the other. You may also measure the resistance of the bleeder resistor like in a multilayer fused microwave.
- Alter the leads by reversing them. Make sure that the meter wards off the zero value gradually and returns to infinity.
- You have to alter the leads again. The same result for the meter is required.
- Measure the infinity of each terminal in the capacitor. Remember that if there is an internal diode, the meter will reflect a bias resistance.
- Defects in the parts can be detected through any or all of the following results through visual inspection: (a) burning site in the insulators; (b) oily film as well as an oily smell hints at a dielectric leak; and (c) bulging case shows a dielectric breakdown.
- Once you are done with the inspections, presence of any or all of the above mentioned defects in the vishay or ceramic components or abnormal meter readings indicate the necessity to install a new capacitor.
With these tips, you are now ready to test the capacitor of one of the most harmful electronic appliances invented.