Troubleshooting Guide - Sharp R-937 Service Manual

THERMISTOR
ON
OFF
ON
Sensing
Voltage
OFF
Sensing the voltage across temperature measurement circuit.
OPEN JUDGE BY THERMISTOR
1. If the temperature of the thermistor does not rise to
more than 40˚C after 4 minutes and 15 seconds from
when the oven is started in convection, grill or dual
cooking mode, the oven is turned off.
2. When the thermistor or the wire harness to the ther-
mistor is opened, the oven is turned off after 4 minutes
and 15 seconds because this condition is same as
above.
DAMPER OPEN-CLOSE MECHANISM
Damper position is set automatically by damper motor
DM, damper switch and motor cam.
These components are operated by a signal that judges
if microwave cooking or convection cooking operation is
selected by the CPU unit.
Microwave Cooking:
Damper is in the open position, because a portion of
cooling air is channelled through the cavity to remove
steam and vapours given off from the heating foods.
It is then exhausted at the top of the oven cavity into a
condensation compartment.
Convection Cooking:
Damper is in the closed position, so that no hot air will be
allowed to leak out the oven cavity.
Damper Operation
1. When power supply cord is plugged in or when the
control unit resumes after energy save mode finishes:
1-1. When power supply cord is plugged in, a signal is
sensed in the control unit, and operates shut-off
relay (RY8).
1-2. Contacts of shut-off relay (RY8) close, the damper
motor DM is energized, opening the damper door.
When troubleshooting the microwave oven, it is helpful to
follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a
specific test be performed. These tests are given a proce-
dure letter which will be found in the "Test Procedure"
section.
OPERATION SEQUENCE
30 32 (sec.)

TROUBLESHOOTING GUIDE

1-3. When the damper is moved to the open position by
the damper cam, damper switch SW4 is closed (ON
position).
1-4. The signal of damper switch SW4 is re-sensed in the
control unit and shut-off relay (RY8) is turned off.
1-5. The rated voltage to the damper motor DM is stopped
and the motor turns off.
2. When oven is microwave cooking:
Damper is in the open position
3. When oven is convection cooking:
3-1 Damper motor DM is energized right after the oven is
started.
3-2. When damper is in the closed position (damper
switch SW4 is OFF), its signal is sensed by the control
unit, and shut-off relay (RY8) is de-energized.
3-3. The damper is held in the closed position during the
convection cooking operation.
3-4. At the end of the convection cooking, when the fan
motor FM stops, shut-off relay (RY8) is energized,
and the damper is returned to the open position.
NOTE: If the damper door is not in the proper position,
closed during convection, grill or dual, or open
during microwave, the control unit will stop oven
operation after 1 minute.
4. Operation of damper is shown below.
Cooking Mode
Microwave cooking
Convection cooking
Grill; during backed up with
convection heating element
Grill; after convection heating
element backed up has stopped
Dual (Microwave and Convection)
Dual (Microwave and Grill)
Fire sensing condition
IMPORTANT: If the oven becomes inoperative because
of a blown fuse F2 (F8A) in the monitored
latch switch SW1 - monitor switch SW3
circuit, check the monitored latch switch
SW1 and monitor switch SW3 before re-
placing the fuse F2 (F8A).
12
Operation of Damper
Open
Closed
Closed
Open
Closed
Open
Closed