Sharp R-1880LS Service Manual page 22

R-1880LS/LST
PROCEDURE
LETTER
A MAGNETRON ASSEMBLY TEST
1. Disconnect the power supply cord, and then remove outer case.
. Open the door and block it open.
3. Discharge high voltage capacitor.
4. 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.
5. 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.
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.
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.
. Place the cup of water in the oven. Operate oven at POWER 10(HIGH) 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 1 to
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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 10 volts and the
oven cavity is clean.
B POWER TRANSFORMER TEST
1. Disconnect the power supply cord, and then remove outer case.
. Open the door and block it open.
3. Discharge high voltage capacitor.
4. 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
less than 1 ohm and the resistance of the high voltage coil should be approximately 13 ohms; the resistance
of the filament coil should be less than 1 ohm.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
(HIGH VOLTAGES ARE PRESENT AT THE HIGH VOLTAGE TERMINAL, SO DO NOT ATTEMPT TO
MEASURE THE FILAMENT AND HIGH VOLTAGE.)
TEST PROCEDURES
O F(11.7 to 1.7 O ) rise in temperature. If the water temperatures are accurately measured and tested for the
COMPONENT TEST