R-852 (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 12

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R-852 - 10
DOOR OPEN MECHANISM
The door can be opened by pushing the open button on the
control panel. When the open button is pushed, the open
lever is pushes lower latch head on the door upward.  The
upper latch head is linked with the  lower latch head, so
now, the door can be opened.
Figure D-1. Door Open Mechanism
MONITORED LATCH SWITCH SW1
1. When the oven door is closed, the contacts (COM-NO)
of the switch must be closed. And the contacts (COM-
NC) must be opened.
2. When the oven door is opened, the contacts (COM-
NO) of the switch must be opened. And the contacts
(COM-NC) must be closed.
STOP SWITCH SW2
1. When the oven door is closed, the contacts (COM-NO)
of the switch must be closed.
2. When the oven door is opened, the contacts (COM-
NO) of switch must be opened.
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 con-
tacts (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  MONITOR SWITCH
SW3  FOR PROPER OPERATION.  (REFER
TO CHAPTER “TEST PROCEDURE”).
FUSE F1 20A 250V
If the wire harness or electrical components are short-
circuited, this fuse F1 blows to prevent an electric shock of
fire hazard.
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 the monitored latch switch
SW1 remains closed with the oven door open and
when the monitor switch SW3 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 trans-
former is shorted.
TC TRANSFORMER
T/C transformer converts A.C. line voltage into low voltage
to drive the control unit.
THERMAL CUT-OUT TC1 125˚C  (MG)
This thermal cut-out protects the magnetron against over-
heat. If the temperature goes up higher than 125˚C be-
cause the fan motor is interrupted or the ventilation open-
ings are blocked, the thermal cut-out TC1 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.
THERMAL CUT-OUT TC2 150˚C (OVEN)
This thermal cut-out protects the oven against the over-
heat during grill cooking, convection cooking or dual
(combination) 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 all the electrical
parts. When the cools itself down to the operating tem-
perature of 130˚C, the contacts of the thermal cut-out will
close again.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is solid state device that prevents
current flow is both directions. And it prevents the tem-
perature rise of the high voltage transformer by blowing
the fuse F2 F8A when the high voltage rectifier is shorted.
FUNCTION OF IMPORTANT COMPONENTS
A
B
C
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
DOOR
LATCH HOOK
SW3: MONITOR SWITCH
SW1: MONITORED
LATCH SWITCH
SW2: STOP SWITCH
OPEN LEVER
LATCH
HEADS
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 some fault when
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