Chapter 8. Test Procedures; A: Magnetron Assembly Test; B: Power Transformer Test; C: High Voltage Rectifier Test - Sharp R-231NW Service Manual

R-231NW

CHAPTER 8. TEST PROCEDURES

[1] Procedure A : MAGNETRON ASSEMBLY 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. To test for an open fi lament, isolate the magnetron from the high voltage circuit. A continuity check across the magnetron fi lament
leads should indicate less than 1 ohm.
5. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron fi lament leads and chassis ground. This test
should indicate an infi nite 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.
1. MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fi tted).
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 rectifi er, high voltage ca-
pacitor 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 thermo
couple temperature tester. Stir the thermometer or thermocouple through the water until the temperature stabilizes. Record the tem-
perature of the water.
2. Place the cup of water in the oven. Operate oven at P-HI (100% Power) 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 20 to 38°F(11.1 to 21.1°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 be-
yond the normal limits. The test is only accurate if the power supply line voltage is 120 volts and the oven cavity is clean.
[2] Procedure B : POWER TRANSFORMER 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 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 202 ohms (RTRN-A727WRZZ) or 190 ohms (RTRN-A728WRZZ); the resistance of the
fi lament 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.)
[3] Procedure C : HIGH VOLTAGE RECTIFIER 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. Isolate the rectifi er from the circuit. Using the highest ohm scale of the meter, read the resistance across the terminals and observe,
reverse the leads to the rectifi er terminals and observe meter reading. If a short is indicated in both directions, or if an infi nite resist-
ance is read in both directions, the rectifi er is probably defective and should be replaced.
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.
NOTE: Be sure to use an ohmmeter that will supply a forward bias voltage of more than 6.3 volts.
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