Sharp R-55TS Service Manual page 19

PROCEDURE
LETTER
7. If the results of above test 5 and/or 6 are out of above specifications, the heater is probably faulty
and should be replaced.
8. Reconnect all leads removed from components during testing.
9. Reinstall the outer case (cabinet).
10.Reconnect the power supply cord after the outer case is installed.
11.Run the oven and check all functions.
J THERMISTOR TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect connector-C from the control unit. Measure the resistance of the thermistor with an
ohmmeter. Connect the ohmmeter leads to Pin No's 1 and 2.
5. If the meter does not indicate above resistance, replace the thermistor
6. Reconnect all leads removed from components during testing.
7. Reinstall the outer case (cabinet).
8. Reconnect the power supply cord after the outer case is installed.
9. Run the oven and check all functions.
K CHECKING TEMPERATURE IN THE PREHEAT OF BAKE 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 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. 30˚F more or less than indicated on the display, however, in most cases the food cooking results
will be satisfactory.
Difference in power supply voltage will also affect the oven temperature. The Household power supply
voltage may sometimes become lower than the rated voltage (120 V) and cause under-cooking. If the power
supply voltage is 10% lower than the rated voltage, longer cooking time is required by 10% to 20%.
L CONTROL UNIT TEST
The control unit consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike
conventional microwave ovens, proper maintenance cannot be performed with only a voltmeter and
ohmmeter.
In this service manual, the control unit is divided into two units, Power Unit and Switch Unit, and
troubleshooting by unit replacement is described according to the symptoms indicated.
Before testing,
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Disconnect the leads to the primary of the power transformer.
5) Ensure that these leads remain isolated from other components and oven chassis by using
insulation tape.
1. Switch Unit.
NOTE ;
1) Re-install the outer case (cabinet).
2) Reconnect the power supply cord after the outer case is installed.
TEST PROCEDURES
COMPONENT TEST
Room Temperature
68˚F(20˚C) - 86˚F(30˚C)
17
Resistance
Approx. 293kΩ - 184KΩ
R-55TS