Sharp R-90GCH Service Manual page 21

PROCEDURE
LETTER
2. Disconnect the leads to the primary of the high voltage transformer.
3. Ensure that the leads remain isolated from other components and oven chassis by using insulation
tape.
4. Disconnect the wire leads from the switch terminals and connect ohmmeter leads to the common
(COM.) and normally open (N.O.) terminals of the switch.
4-1. When switch actuator is pushed by the damper motor cam, the meter should be indicated a
closed circuit.
4-2. When power cord is plugged into the wall receptacle, the damper motor operates and damper
cam will start to rotate. When the switch actuator is released, the meter should be indicated an
open circuit.
5. If improper operation is indicated, replace the damper switch.
6. Disconnect the oven from power supply, and then remove outer case.
7. Open the door and wedge it open.
8. Discharge high voltage capacitor.
9. CARRY OUT 4R CHECKS.
R CONVECTION MOTOR CAPACITOR C2 TEST
1. CARRY OUT 3D CHECKS.
2. Disconnect input leads and check for short or open between the terminals using an ohmmeter.
Checking with a high ohm scale, if the capacitor is normal, the meter will indicate continuity for a
short time and should indicate an open circuit once the capacitor is charged. If the above is not
the case, check the capacitor with an ohmmeter to see if it is shorted between the terminals. If it
is shorted, replace the capacitor.
3. CARRY OUT 4R CHECKS.
S CONVECTION MOTOR CM TEST
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
3. Disconnect the 3-pin connector of the convection motor from the main wire harness.
4. Measure the resistance of the convection motor with an ohmmeter.
The resistance of the main coil, across the black and the red wires, should be approximately 130
ohms. The resistance of the sub coil, across the black and the white wires, should be
approximately 140 ohms.
5. Also, the convection motor has the thermal cut-out in it.
Measure the resistance of the main coil (or the sub coil). The resistance across the black and the
red wires (or across the black and the white wires) should be above resistance unless the
temperature of the thermal cut-out reaches approximately 130˚C. The thermal cut-out resets
automatically at 100˚C. If an ohmmeter indicates
an open circuit under normal condition, replace
the convection motor because the thermal cut-
out has opened. An open thermal cut-out
indicates overheating of the convection motor.
Check for restricted air flow to the convection
motor or a lock of the convection fan, especially
the fan motor (high voltage transformer side).
6. CARRY OUT 4R CHECKS.
T CHECKING TEMPERATURE IN THE CONVECTION MODE
The following test procedure should be carried out with the microwave oven is a fully assembled
condition (outer case fitted).
It is difficult to measure the exact temperature in the convection oven. An accurate thermocouple type
temperature tester must be used. A low priced bi-metal type thermometer is not reliable or accurate.
The temperature should be checked with outer case cabinet installed, approx. 5 minutes after preheat
temperature is reached (audible signal sounds four times). The temperature experienced may be
approx. 17˚C more or less than indicated on the display, however, in most cases the food cooking
results will be satisfactory.
TEST PROCEDURES
COMPONENT TEST
19
Main Coil
Thermal
130Ω
Cut-out
140Ω
130˚C OFF
100˚C ON
Sub Coil
CONVECTION MOTOR
R-90GCH
3-pin
Connector
BLK
RED
WHT