Sharp R-4A68, Service Manual

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R-4A68
5
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The door can be opened by pushing the door open button on
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
HEADS
LATCH HOOK
2ND. INTERLOCK
RELAY CONTROL
SWITCH
MONITOR
SWITCH
SWITCH LEVER
1ST. LATCH
SWITCH
Figure D-1. Door Open Mechanism
1ST. LATCH SWITCH AND 2ND. INTERLOCK RE-
LAY CONTROL 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. interlock relay 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. IN-
TERLOCK RELAY, 2ND. INTERLOCK RELAY
CONTROL SWITCH, MONITOR SWITCH AND
MONITOR RESISTOR FOR PROPER OP-
ERATION. (REFER TO CHAPTER “TEST
PROCEDURE”.)
MONITOR RESISTOR (0.8
Ω
20W)
The monitor resistor prevents the fuse (M8A) bursting when
the fuse blows due to the operation of the monitor switch.
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 improper
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 defective
thermal cut-out must be replaced with new one.
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 also blows when the contacts (COM-NO) of the
1st. latch switch and 2nd. interlock relay remain closed
with the oven door open and then the monitor switch
closes.
TEMPERATURE FUSE 150˚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.
FAN MOTOR
The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and va-
pours given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly to
rotate the turntable.