Test Procedure - Sharp R-8000G Service Manual

PROCEDURE
LETTER
A MAGNETRON ASSEMBLY TEST
1. Disconnect the power supply cord.
2. Remove the outer case cabinet, referring to "OUTER CASE CABINET REMOVAL".
3. Open the oven door and block it open.
4. Discharge the high voltage capacitor.
5. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
6. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check across
the magnetron filament leads should indicate less than 1 ohm.
7. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads and
chassis ground. This test should indicate an infinite resistance. If there is little or no resistance the
magnetron is grounded and must 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.
MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled condition
(outer case fitted).
HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE, SO EXTREME CAUTION SHOULD BE
OBSERVED.
Power output of the magnetron can be measured by performing a water temperature rise test. This test should
only be used if above tests do not indicate a faulty magnetron and there is no defect in the following
components or wiring: silicon rectifier, high voltage capacitor and power transformer. This test will require a
16 ounce (453cc) measuring cup and an accurate mercury thermometer or thermocouple type temperature
tester. For accurate results, the following procedure must be followed carefully:
1. Fill the measuring cup with 16 oz. (453cc) of tap water and measure the temperature of the water with a
thermometer or thermocouple temperature tester. Stir the thermometer or thermocouple through the water
until the temperature stabilizes. Record the temperature of the water.
2. Place the cup of water in the oven. Operate oven at HIGH POWER (100%) selecting more than 60 seconds
cook time. Allow the water to heat for 60 seconds, measuring with a stop watch, second hand of a watch
or the digital read-out countdown.
3. Remove the cup from the oven and again measure the temperature, making sure to stir the thermometer
or thermocouple through the water until the maximum temperature is recorded.
4. Subtract the cold water temperature from the hot water temperature. The normal result should be 29.5 to
54.9˚F(16.4 to 30.5˚C) rise in temperature. If the water temperatures are accurately measured and tested
for the required time period the test results will indicate if the magnetron tube has low power output (low
rise in water temperature) which would extend cooking time or high power output (high rise in water
temperature) which would reduce cooking time. Because cooking time can be adjusted to compensate for
power output, the magnetron tube assembly should be replaced only if the water temperature rise test
indicates a power output well beyond the normal limits. The test is only accurate if the power supply line
voltage is 240 volts and the oven cavity is clean.
B POWER TRANSFORMER TEST
1. Disconnect the power supply cord.
2. Remove the outer case cabinet, referring to "OUTER CASE CABINET REMOVAL".
3. Open the oven door and block it open.
4. Discharge the high voltage capacitor.
5. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
6. Disconnect the primary input terminals and measure the resistance of the transformer with an ohmmeter.
Check for continuity of the coils with an ohmmeter. On the R x 1 scale, the resistance of the primary coil
should be approximately 0.9 ohms and the resistance of the high voltage coil should be approximately 67
ohms; the resistance of the filament coil should be less than 1 ohm.
7. Also, the power transformer has the thermostat in the primary coil. Measure the resistance of the primary
coil. The resistance of the primary coil should be above resistance unless the temperature of the thermostat
in the primary coil reaches approximately 320˚F (160˚C). The thermostat resets automatically at
221˚F(105˚C). If an ohmmeter indicates an open circuit under normal condition, replace the power
TEST PROCEDURES
COMPONENT TEST
15
R-8000G