Sharp R-9320 Service Manual page 33

TEST PROCEDURES
ROCEDURE 1
LETTER 1
COMPONENT TEST
A ~
MAGNETRON ASSEMBLY TEST
I
i 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
i 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
j chassis ground. This test should indicate an infinite resistance. If there is little or no resistance, the magne-
: tron is grounded and must be replaced.
I
1 Power out.put 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, heater transformer 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 (W) heating works for t (second), approximately P*t/4.2 calorie is generated. On the other hand, if
the temperature of the water with V (ml) rises AT ("C) during this microwave heating period, the calorie of
the water is V *AT.
The formular is as follows;
P-t
- =V*AT
4.2
P
4.2
l
V
l
AT
=
t
NV)
Our condition for the water load is as follows;
Water load . . . . .2OOO ml
Heating time . . . 120 seconds (2 minutes)
Measuring method;
1. Put the water load of two (2) litres on the center 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 aher heating during two minutes by micro-
wave, 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 215% of the nominal one.
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