R-875/885 -
13
DOOR OPEN MECHANISM
The door can be opened by pulling the door handle. When the
handle is pulled, the latch head is pulled, the latch head is moved
upward, and released from the latch hook 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 lower
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. At this time the contacts (COM-NO) of
monitored latch switch SW1 are open.
2. As the door closed, the monitor switch SW3 contacts (COM-
NC) are opened and contacts (COM-NO). The 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 transformer 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 overheat.
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 TC1 will open and the oven will switch off. The
defective thermal cut-out must be replaced with a new one.
THERMAL CUT-OUT TC2 145
˚
C (OVEN)
This thermal cut-out protects the oven against overheating or fire
inside the oven. If the temperature rises above 145
˚
C the thermal
cut-out opens the oven will switch off. When the cut-out cools
down to the operating temperature of 115
˚
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 temperature
rise of the high voltage transformer by blowing the fuse F2 F8A
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 fuse F2 F8A.)
1. The high voltage rectifier is shorted by some fault 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.
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 interference
that might flow back in the power circuit.
TURNTABLE MOTOR TTM
The turntable motor rotates the turntable.
Latch hook
Door
SW2: Stop switch
Latch
Heads
SW3: Monitor switch
SW1: Monitored
latch switch
Tab
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
FUNCTION OF IMPORTANT COMPONENTS
