Sharp R-990C Service Manual page 21

PROCEDURE
LETTER
To determine if the sensor is defective, the simplest method is to replace it with a new replacement
sensor.
(1) Disconnect oven from power supply and remove outer case.
(2) Discharge the high voltage capacitor.
(3) Remove the AH sensor.
(4) Install the new AH sensor.
(5) Re-install the outer case.
(6) Reconnect the oven to the power supply and check the sensor cook operation, proceed as follows:
6-1. Fill approximately 200 milliliters (7.2 oz) of tap water in a 1000 milliliter measuring cup.
6-2. Place the container on the center of tray in the oven cavity.
6-3. Close the door.
6-4. Touch REHEAT SENSOR pad twice and touch the INSTANT COOK/START pad.
6-5. The control panel is in automatic Sensor operation.
6-6. The display will start to count down the remaining cooking time, and the oven will turn off
automatically after the water is boiling (babbling).
If new sensor dose not operate properly, the problem is with the control unit.
(1) Disconnect oven from power supply and remove outer case.
(2) Discharge the high voltage capacitor.
(3) Disconnect the wire leads from the cook relay.
(4) Disconnect the sensor connector that is mounted to lower portion of control panel.
(5) Then connect the dummy resistor circuit (see fig.) to the sensor connector of control panel.
(6) Reconnect the oven to the power supply and check the sensor cook operation, proceed as follows:
6-1. Touch REHEAT SENSOR pad twice and touch the INSTANT COOK/START pad.
6-2. The control panel is in the sensor cooking operation.
6-3. After approximately 20 seconds, push plunger of select switch. This condition is same as
judgement by AH sensor.
6-4. After approximately 3 seconds, the display shows " X X . X X " which is the remaing cooking
time, and the display counts down.
If the above is not the case, the control unit is probably defective.
If the above is proper, the AH sensor is probably defective.
TEST PROCEDURES
TESTING METHOD FOR AH SENSOR AND/OR CONTROL UNIT
CHECKING CONTROL UNIT
To connector (F)
on Control Unit.
1
F-1
2
F-2
3
F-3
CONNECTOR
R1,R2 : 22
Sensor Dummy Resistor Circuit
19
COMPONENT TEST
R1
R3 R4
R2
1% 1/2W
R3 : 4.3k 5% 1/4W
R4 : 1M 5% 1/4W
R-990C(S)
Plunger
NC
NO
COM
NO
COM
NC