Function Of Important Components - Sharp R-390B Service Manual

R-390B
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 latch heads. The latch heads are moved upward and
released from latch hook. Now the door will open.
Door
Latch
Heads
Switch
Lever
Stop
Switch
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,
LATCH SWITCH MONITOR SWITCH AND
MONITOR RESISTOR FOR PROPER OP-
ERATION.
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.
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.
D2 D1
ASYMMETRIC
RECTIFIER

FUNCTION OF IMPORTANT COMPONENTS

Latch Hook
2nd. Latch
Switch
Monitor
Switch
1st. Latch
Switch
2ND.
HIGH VOLTAGE
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 1.7KV. 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 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 all the 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.
OVEN THERMAL CUT-OUT
The thermal cut-out, located on the top of the oven cavity,
is designed to prevent damage to the oven by fire. If the
foods load is overcooked, by either error in cook time or
defect in the control unit, the thermal cut-out will open.
Under normal operation, the oven thermal cut-out remains
closed. However, when abnormally high temperature is
reached within the oven cavity, the oven thermal cut-out
will open at 125˚C, causing the oven to shut down. The
defective thermal cut-out must be replaced with new one.
MAGNETRON THERMAL CUT-OUT
The thermal cut-out located near the magnetron is de-
signed to prevent damage to the magnetron if an over
heated condition develops in the tube due to cooling fan
failure, obstructed air guide, dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains
closed. However, when abnormally high temperature is
reached within the magnetron, the thermal cut-out will
open at 95˚C causing the oven to shut down, when the
magnetron has cooled to 75˚C, the thermal cut-out closes
and cook cycle will resume.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly to
rotate the turntable.
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