Sharp R-84ST Service Manual page 12

MONITOR SWITCH SW3
The monitor switch is activated (the contacts opened) by the
upper latch head on the door while the door is closed. The switch
is intended to render the oven inoperative by means of blowing
the fuse F2 F8A when the contacts of the monitored latch switch
SW1 fail to open when the door is opened.
Function
1. When the door is opened, the contacts (COM-NC) of
monitor switch SW3 close (to the ON condition) due to their
being normally closed and contacts (COM-NO) open. At
this time the contacts (COM-NO) of monitored latch switch
SW1 is in the OFF condition (contacts open) due to their
being normally open contact switches.
2. As the door goes to a closed position, the monitor switch
SW3 contacts (COM-NC) are opened and contacts (COM-
NO) closed and then contacts (COM-NO) of monitored
latch switch SW1 and stop switch SW2 are closed.(On
opening the door, each of these switches operate inversely.)
3. If the door is opened and the monitored latch switch SW1
contacts (COM-NO) fail to open, the fuse F2 (F8A) blows
immediately after closing of the monitor switch (COM-NC)
contacts.
CAUTION: BEFORE REPLACING A BLOWN FUSE F2
F8A, TEST THE MONITORED LATCH SWITCH
SW1 AND
PROPER OPERATION. (REFER TO CHAP-
TER "TEST PROCEDURE").
FUSE F2 F8A 250V
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 monitored latch switch SW1
remains closed with the oven door open and when the
monitor switch SW2 contact (COM-NC) closes.
3. The fuse also blows when the asymmetric rectifier, H.V.
rectifier,.H.V. wire harness, H.V. capacitor, magnetron or
secondary winding of high voltage transformer is shorted
TC TRANSFORMER
TC transformer converts A.C. line voltage into low voltage to
drive the control unit.
THERMAL CUT-OUT TC1 150˚C (OVEN)
The thermal cut out protects the oven against overheat
during grill cooking, convection cooking or dual (combina-
tion) cooking. If the temperature rises above 150˚C because
the fan motor is interrupted, the air inlet duct is blocked or the
ventilation openings are obstructed, the thermal cut-out
opens and switches off the all electrical parts.
When the oven cools itself down to the operating tempera-
ture of 130˚C, the contacts of the thermal cut-out will close
again.
THERMAL CUT-OUT TC2 125˚C (MG)
This thermal cut-out protects the magnetron against over-
heat. If the temperature goes up higher than 125˚C because
the fan motor is interrupted or the ventilation openings are
blocked, the thermal cut-out TC2 will open and line voltage
to the high voltage transformer T will cut off and operation of
the magnetron MG will be stopped. The defective thermal
cut-out must be replaced with a new one.
FUNCTION OF IMPORTANT COMPONENTS
MONITOR SWITCH SW3
R-84ST -
ASYMMETRIC RECTIFIER
The asymmetric rectifier is solid state device that prevents
current flow is both directions. And it prevents the tempera-
ture rise of the power transformer by blowing the fuse F2 F8A
when the high voltage rectifier is shorted.
ASYMMETRIC
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
peak reverse voltage goes beyond the each rated peak
reverse voltage. (The process of the blowing the fuse F2
F8A.)
1. The high voltage rectifier is shorted by any causes when
microwave cooking or dual 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.
FOR
4. The large electric currents flow through the high voltage
winding of the high voltage transformer.
5. The large electric currents beyond 8A flow through the
primary winding of the high voltage transformer.
6. The fuse F2 F8A blows by the large electric currents.
7. The power supplying to the high voltage transformer is
cut off.
NOISE FILTER
The noise filter assembly prevents radio frequency interfer-
ence that might flow back in the power circuit.
TURNTABLE MOTOR TTM
The turntable motor drives the roller stay to rotate the
turntable.
FAN MOTOR FM
The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding the
magnetron and cools the magnetron. This air is channeled
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.
CONVECTION MOTOR CM
The convection motor drives the convection fan and provide
the heated air.
TOP GRILL HEATING ELEMENT GH
The grill heating element is provided to brown the food and
is located on the top of the oven cavity.
BOTTOM GRILL HEATING ELEMENT BH
The grill heating element is provided to brown the food and
is located at the base of the oven cavity.
12
D2 D1
HIGH VOLTAGE RECTIFIER
C