High Voltage Microwave Oven Fuse 0.8A 5 kV

High Voltage Microwave Oven Fuse 0.8A 5 kV

 When your microwave oven stopped to warm up food, first thing what you want to do, go shopping and get the new one.

But, wait a minute, just realised that you bought that one 18 months ago.

You spent a lot of money, warranty on appliance just finished and stopped work.

When your appliance seams working fine, but the food is still cold.

Your appliance is broken.

In 90% of faulty microwave ovens when food is not warmed up as should be happened, burned high voltage fuse is responsible for that (most appliances sold in UK and EU).

Some microwave ovens haven't high voltage fuse.

All work with microwave oven should be carried out by the qualified technician or person who knows how to deals with electrics.

Microwave ovens are among the most dangerous appliances to work on.

Before attempting any troubleshooting, testing or repairs, for your personal safety, we strongly urge you:

-disconnect from mains

-discharge capacitor

- do not do any measurements on high voltage side of the transformer when appliance connected to the mains

-high voltage in the microwave oven is about 4200V

-do not touch any conductive wires on HV side, even by the insulated screwdriver

- do not measure a voltage on the secondary winding

The capacitor can store the electric charge that can be dangerous to health and life.

High voltage capacitor is placed in the plastic tube (black or white), mounted on one of the second wiring connectors.

Second wire of fuse is connected to the high voltage capacitor.

Open the tub, need the flat screwdriver.

Check if fuse need replace.

If the fuse is ok, need to check high voltage capacitor.

The high-voltage capacitor works together with the high voltage diode to double high voltage from 2100V secondary (output) winding of the power transformer to 4200V on the magnetron.

This high voltage gets the magnetron into oscillation. 

To discharge capacitor you need to create a short circuit between the two capacitor terminals and from each terminal to chassis.

1. Do this by touching the blade of an insulated screwdriver to one terminal, then slide it toward the other terminal until it makes contact and holds it there for a few seconds.
   
2.  Note: If there is a spark, the capacitor is holding a charge, not defective
3. Repeat the procedure to create a short between each capacitor terminal and chassis ground.
4. Usually, capacitors do not store charge if the fuse was burned, but for your safety before the check, fuse have to discharge the capacitor.
   

Ground each magnetron terminal by creating a short circuit to chassis ground using the blade of a screwdriver as explained above.

How to test capacitor.

1. Unplug the oven.
2. DISCHARGE ALL HIGH VOLTAGE CAPACITORS.
3. Note the wiring and carefully remove all leads from the capacitor terminals. If there is a resistor connected to the HV capacitor, it not necessary to be removed but, some results of measurements can be changed by resistance of the resistor
4. Set the ohmmeter to its highest resistance scale.
5. Measure from one terminal to the other for a normal reading of infinity (or the value of the resistor).
6. Now reverse the leads. The meter should momentarily deflect toward the zero mark, then slowly drift back to infinity.
7. Reverse the leads once again. This should produce the same meter deflection.
8. Next measure from each terminal to the capacitor's metal case for a normal reading of infinity. (If there is an internal diode, the meter readings will reflect the diode's forward bias resistance.
9. A visual inspection will also reveal certain defects, such as:

• Evidence of arcing or burning at the insulators
• The presence of an oily film or smell suggests a dielectric (non-conductive medium) leak
• A bulging case indicates dielectric breakdown

Test Procedure

1. Unplug the oven.
2. DISCHARGE ALL HIGH VOLTAGE CAPACITORS. (Procedure)
3. Carefully remove the lead that goes to the capacitor (the ground connection may remain attached)
4. Set the ohmmeter to read ohms at a scale of R X 10,000 or higher.
5. Measure the resistance across the terminals of the diode by touching the positive meter probe to the anode and the negative probe to the cathode (the cathode is the side that goes to ground, usually marked by an arrow, dot or stripe).
6. A normal diode, depending on make and model, should read about 50,000 to 200,000 ohms.
   (Note: The polarity of the meter probes, with regard to forward and reverse bias readings, may be relative to the type of meter being used.)
7. Reversing the leads should produce a reading of infinity (open) unless there is a bleeder resistor across the diode, in which case the reading would show the [megohm] value of the resistor.
8. If continuity is read in both directions, the diode is shorted. If infinity is read in both directions, the diode is open. In each case, the diode must be replaced.

In some models, the diode is located inside of the high voltage capacitor. In this case, identify the diode terminal and perform the same test as above, measuring from the diode terminal to the capacitor's metal case.