Sharp R-8320E, Service Manual

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TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
7
A
MAGNETRON ASSEMBLY TEST
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN
COMPONENTS OR WIRING.
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.
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.
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: rectifier, high voltage capacitor and power transformer.
MICROWAVE OUTPUT POWER
Microwave output power from the magnetron can be measured by way of substitution, i.e. it can be
measured by using water load how much it can be absorbed by the water load. To measure the
microwave output power in the microwave oven, the relation of calorie and watt is used.
When P heating works for t (second), approximately calorie is generated. On the other
hand, if the temperature of the water with V (ml) rises
AT
during this microwave heating
period, the calorie of the water is
V-AT.
The formular is as follows;
4.2.V-AT
- - -
Our condition for the water load is as follows;
water load . . . . ml
Heating time. . . seconds (2 minutes)
Measuring method;
1. Put the water load of two (2) litres on the
of the oven shelf.
The water load should be arranged in two (2) Pyrex beakers, the size of which is one (1) litre,
and be placed at right and left, side by side, on the oven shelf.
2. Measure the temperature of water before heating and also after heating during two minutes by
microwave, and calculate the temperature rise.
The temperature rise should be the average of temperature differences measured in each beaker.
3. The output power should be calculated as follows.
In case the measuring result is not satisfactory, execute the measurement several times and judge
the result from the synthetic point of view.
Microwave output power should be within of the nominal one.
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