Function Of Important Components - Sharp R-3A56 Service Manual

DOOR OPEN MECHANISM
The door is opened by pushing the open button on the
control panel, refer to the Figure D-1.
When the open button is pushed, the open button pushes up
the switch lever, and then the switch lever pushes up the the
latch head. The latch heads are moved upward and re-
leased from latch hook. Now the door will open.
LATCH HOOK
LATCH
HEADS
SWITCH
LEVER
Figure D-1. Door Open Mechanism
1ST. LATCH SWITCH, 2ND. 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 1st. latch switch and 2nd. latch switch fail to open,
the fuse M8A blows simultaneously with closing the
contacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE M8A
TEST THE 1ST. LATCH SWITCH, 2ND. LATCH
SWITCH MONITOR SWITCH AND MONITOR
RESISTOR FOR PROPER OPERATION.
MONITOR RESISTOR R 0.8 20W
The monitor resistor prevents the fuse M8A bursting when
the fuse M8A blows due to the operation of the monitor
switch.

FUNCTION OF IMPORTANT COMPONENTS

2ND. LATCH
SWITCH
MONITOR
SWITCH
1ST. LATCH
SWITCH
STOP SWITCH
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that prevents
current flow in both directions. And it prevents the tempera-
ture rise of the power transformer by blowing the fuse M8A
when the high voltage rectifier is shorted.
A
D2 D1
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 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 M8A 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 all electrical parts are cut off.
FUSE M8A
1. The fuse M8A blows when the contacts (COM-NO) of the
1st. latch switch and 2nd. latch switch remain closed with
the oven door open and when the monitor switch closes.
2. The fuse M8A also blows when asymmetric rectifier,
H.V. rectifier, H.V. wire harness, H.V.capacitor,
magnetron or secondary winding of power transformer is
shorted.
3. If the wire harness or electrical components are short-
circuited, this fuse M8A blows to prevent an electric
shock or fire hazard.
THERMAL CUT-OUT TC 145˚C (MG)
This thermal cut-out protects the magnetron against over-
heating. If the temperature goes up higher than 145˚C
because the fan motor is interrupted, the ventilation open-
ings are blocked, the thermal cut-out will open and the line
voltages to the power transformer will be cut off and the
operation of the magnetron will be stopped.
The defective thermal cut-out must be replaced with new
one.
THERMAL CUT-OUT TC 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 improper
setting of cook time or failure of control unit. Under normal
5
B
HIGH VOLTAGE RECTIFIER
C
R-3A56