R939(W)
6 – 1
R939(W)
Service Manual
CHAPTER 6.
FUNCTION OF IMPORTANT COMPONENTS
[1] DOOR OPEN MECHANISM
The door can be opened by pulling the door handle.
When the door handle 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
[2] MONITORED LATCH SWITCH (SW1)
1. When the oven door is closed, the contacts (COM-NO) of the
switch must be closed. And the contacts (COMNC) must be
opened.
2. When the oven door is opened, the contacts (COMNO) of the
switch must be opened. And the contacts (COM-NC) must be
closed.
[3] 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 (COMNO) of switch
must be opened.
[4] 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 con-
tacts (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 SW3 (COM-NC) contacts.
CAUTION: BEFORE REPLACING A NOISE FILTER (BLOWN FUSE
F2 F8A), TEST THE MONITORED LATCH SWITCH SW1
AND MONITOR SWITCH SW3 FOR PROPER OPERA-
TION. (REFER TO CHAPTER “TEST PROCEDURE”).
[5] FUSE (F1) 20A 250V
If the wire harness or electrical components are shortcircuited, this
fuse F1 20A blows to prevent an electric shock of fire hazard.
[6] FUSE (F2) F8A 250V (NOISE FILTER)
1. If the wire harness or electrical components are shortcircuited, 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.
[7] TC TRANSFORMER
T/C transformer converts A.C. line voltage into low voltage to drive the
control unit.
[8] THERMAL CUT-OUT (TC1) 125C (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 switch off all the electrical parts. The defective ther-
mal cut-out must be replaced with a new one.
[9] THERMAL CUT-OUT (TC2) 170C (GRILL)
This thermal cut-out protects the oven against the overheat during grill
cooking, convection cooking or dual cooking. If the temperature rises
above 170
°
C because the fan motor is interrupted, the air inlet duct is
blocked or the ventilation openings are obstructed, the thermal cut-out
TC2 opens and switches off all the electrical parts. When the cut-out
cools itself down to the operating temperature of 155
°
C, the contacts
of the thermal cut-out will close again.
[10] THERMAL CUT-OUT (TC3) 170C
(CONV.)
This thermal cut-out protects the convection motor against overheat-
ing. If the temperature of the thermal cut-out TC3 rises above 170
°
C
because the convection fan is interrupted, the ventilation openings are
obstructed or the other abnormal matter occurs, the thermal cut-out
opens and switches off the convection heating element and the other
electrical parts. When the cut-out cools itself down to the operating
temperature of 155
°
C, the contacts of the thermal cut-out will close
again.
[11] ASYMMETRIC RECTIFIER
The asymmetric rectifier is solid state device that prevents current flow
in both directions. And it prevents the temperature rise of the high volt-
age transformer by blowing the fuse F2 F8A when the high voltage
rectifier is shorted.
Latch hook
Door
SW2: Stop switch
Latch
Heads
SW3: Monitor switch
SW1: Monitored
latch switch
Tab
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE
RECTIFIER
Summary of Contents for R-939(BK)
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