R-4G75M (serv.man7). Complete - Sharp Home Appliance Service Manual (repair manual). Page 9

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ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that prevents
current flow in both directions. And it prevents the temperature
rise of the power transformer by blowing the fuse M8A when
the high voltage rectifier is shorted.

peak reverse voltage goes beyond the each rated peak
reverse voltage.
(The process of blowing the fuse M8A)
1. The high voltage rectifier is shorted by any causes when

microwave cooking.

2. The peak reverse voltage of D2 of the rectifier goes

beyond the rated peak reverse voltage 1.7 KV in the
voltage doubler circuit.

3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage

winding of the power transformer.

5. The large electric currents beyond M8A flow through the

primary winding of the power transformer.

6. The fuse M8A blows by the large electric currents.
7. The power supply to the power transformer is cut off.

Microwave ovens contain circuitry capable of producing very high voltage and current,  contact with following parts:
High voltage capacitor, Power transformer, Magnetron, High voltage rectifier assembly, High voltage harness.

1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.

WARNING AGAINST THE CHARGE OF THE

HIGH-VOLTAGE CAPACITOR

The high-voltage capacitor remains charged about
60 seconds after the oven has been switched off.
Wait for 60 seconds and then short-circuit the
connection of the high-voltage capacitor (that is,
of the connecting lead of the high-voltage recti-
fier) against the chassis with the use of an insu-
lated screwdriver.

REMEMBER TO CHECK 4R
1) Reconnect all leads removed from components

during testing.

2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run and oven. Check all functions.

Microwave ovens should not be run empty. To test for
presence of microwave energy within a cavity, place a
cup of cold water on the oven turntable, close the door
and set the microwave timer for two (2) minutes. Set the
power of level to HIGH and push the START button.
When the two minutes has elapsed (timer at zero)
carefully check that the water is now hot. If the water
remains cold carry out 3D checks and re-examine the
connections to the component being tested.

Sharp recommend that wherever possible fault-finding
is carried out with the supply disconnected. It may in,
some cases, be necessary to connect the supply after
the outer case has been removed, in this event carry out
3D checks and then disconnect the leads to the primary
of the power transformer. Ensure that these leads
remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testing is completed carry out 3D checks and reconnect
the leads to the primary of the power transformer.

When all service work is completed, and the oven is fully assembled, the microwave power output should be checked
and a microwave leakage test carried out.

TROUBLESHOOTING GUIDE

IMPORTANT: If the oven becomes inoperative because

of a blown fuse M8A in the primary latch
switch - monitor switch - monitor resistor
circuit, check the primary latch switch,
monitor switch and monitor resistor before
replacing  the fuse M8A.

When troubleshooting the microwave oven, it is helpful to
follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a
specific test be performed. These tests are given a procedure
letter which will be found in the ”Test Procedure” section.

D2

D1

ASYMMETRIC

RECTIFIER

HIGH VOLTAGE RECTIFIER

The rated peak reverse voltage of D1 of the asymmetric
rectifier is 6 KV. The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmetric
rectifier or high voltage rectifier are shorted when the each