R4H55
R-4X55
R-4X55B
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The door can be opened by pushing the door open button
an the control panel. When the door open button is
pushed, the latch lever is moved upward, operating the
latch head. The latch head is moved upward, and released
from the latch hook. Now, the door can be opened.
LATCH
MONITOR
HOOK \
, SWITCH
UPPER
LATCH
SWITCH
LATCH
HEAD
DOOR
OPEN ’
BUTTON
Figure D-l. Door Open Mechanism
UPPER LATCH SWITCH, LOWER LATCH
SWITCH AND STOP SWITCH
1. When the oven door is closed, the contacts (COM - NO)
must be closed.
2. When the oven door is opened, the contacts (COM -
NO) must be opened.
MONITOR SWITCH
1. When the oven door is closed, the contacts (COM- NC)
must be opened.
2. When the oven door is opened, the contacts (COM-
NC) must be closed.
3. If the oven door is opened and the contacts (COM- NO)
of the upper and lower latch switches fail to open, the
fuse (M8A) blows simultaneously with closing the con-
tacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE
(M8A) TEST THE UPPER AND LOWER
LATCH SWITCHES, MONITOR SWITCH
AND MONITOR RESISTOR FOR PROPER
OPERATION. (REFER TO CHAPTER “TEST
PROCEDURE”.)
MONITOR RESISTOR (0.8$2 20W)
The monitor resistor prevents the fuse (M8A) bursting
when the fuse blows due to the operation of the monitor
switch.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that pre-
vents 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.
/
H;;jH VOLTAGE RECTIFIER
The rated peak reverse voltage of Di of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. Dl and D2 of the asymmet-
ric rectifier or high voltage rectifier are shorted when the
each 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 8A 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.
THERMAL CUT-OUT 145°C (OVEN)
The thermal cut-out located on the top of the oven cavity is
designed to prevent damage to the oven if the foods in the
oven catch fire due to over heating produced by unproper
setting of cook time or failure of control unit. Under normal
operation, the oven thermal cut-out remains closed. How-
ever, when abnormally high temperatures are reached
within the oven cavity, the oven thermal cut-out will open at
145”C, causing the oven to shut down. The thermal cut-out
will be close its contacts again when its temperature goes
down lower than -20°C.
FUSE (M8A)
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 blows when the asymmetric rectifier, H.V.
rectifier, H.V. wire harness, H.V. capacitor, magnetron
or secondary winding of power transformer is shorted.
3. The fuse also blows when upper and lower latch
switches remains closed with the oven door open and
when the monitor switch closes.
TEMPERATURE FUSE 15O’C (MG)
This fuse protects the magnetron against overheating. If
the temperature goes up higher than 150°C because the
fan motor is interrupted, the air inlet duct is blocked or the
ventilation openings are obstructed, the fuse blows and
puts the oven out of operation.
The defective fuse must be replaced with new rated one.
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