R-2287 - Sharp Home Appliance Service Manual (repair manual). Page 8

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The air temperature around the lower magnetron is
detected through the resistance of the thermistor.
If the temperature is high, the control panel will display
"EE17" and the oven will stop to protect the lower magn-
etron against overheat.
If the thermistor is open, the control panel will display
"EE16" and the oven will stop.

These thermal cut-outs protect the magnetrons against
overheat. If their temperature go up higher than 145˚C
because the blower motor is interrupted, the ventilation
openings are blocked, the thermal cut-outs TC1+TC2 will
open and the line voltage to the high voltage transformer
T1+T2 will be cut off and the operations of the magnetrons
MG1+MG2 will be stopped. The defective thermal cut-out
must be replaced with new rated one.

This thermal cut-out protect the blower motor against
overheat. If its temperature goes up higher than 115˚C
because the blower motor is locked or the ventilation
openings are blocked, the contacts of the thermal cut-out
TC3 will open and the line voltage to the control unit will
be cut off and the operation of the oven will be stopped.
The defective thermal cut-out must be replaced with new
rated one.

This 

thermal cut-out

 protects the oven against overheat. If

the temperature goes up higher than 115˚C because the
food catches fire, the contacts of 

thermal cut-out

 will open

and the line voltage to the control unit will be cut off and the
operation of the oven will be stopped. The defective 

thermal

cut-out

 must be replaced with a new rated one.

The blower motor drives a blade which draws external
cool air. This cool air is directed through the air vanes
surrounding the magnetrons and cools the magnetrons.
This air is channelled through the oven cavity to remove
steam and vapours given off from the heating foods. It is
then exhausted through the exhausting air vents at the
oven cavity.

The stirrer motor drives a stirrer antenna to stir the
microwave radiation from the waveguide.

1. If the wire harness or electrical components are short-

circuited, this fuse blows to prevent an electric shock
or fire hazard.

2. The fuse also blows when 1st latch switch SW1

remains closed with the oven door open and when the
monitor switch SW4 closes.

The asymmetric rectifier is solid state device that pre-
vents current flow is both directions. And it prevents the
temperature rise of the high voltage transformer by
blowing the weak point / fuse WP1 or WP2 when the high
voltage rectifier is shorted.

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 peak reverse voltage goes beyond the
each rated peak reverse voltage. (The process of the
blowing the weak point / fuse WP1 or WP2)
1. The high voltage rectifier is shorted by some fault

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 high voltage transformer.

5. The large electric currents flow through the primary

winding of the high voltage transformer.

6. The weak point/ fuse WP1 or WP2 blows by the large

electric currents.

7. The power supplying to the high voltage transformer

is cut off.

The thermistor is a negative temperature coefficient type.
The temperature in the exhaust duct is detected through
the resistance of the thermistor.
If the temperature is high, the control panel will display
“EE7” and the oven will stop to avoid overheating and
catching fire.
If the thermistor is open, the control panel will display
"EE6" and the oven will stop.

This thermistor detects ambient air temperature.