Test Procedure - Sharp R-90GCH Service Manual

R-90GCH
PROCEDURE
LETTER
A MAGNETRON ASSEMBLY TEST
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
3. 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.
4. 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.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet) and the back plate.
7. Reconnect the power supply cord after the outer case and back plate are installed.
8. Run the oven and check all functions.
MICROWAVE OUTPUT POWER (IEC60705)
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (outer case fitted). Microwave output power from the magnetron can be measured by IEC
60705, 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 x t/4.187 calorie is generated. On the
other hand, if the temperature of the water with V(ml) rises ∆T (˚C) during this microwave heating
period, the calorie of the water is V x ∆T.
The formula is as follows;
P x t / 4.187 = V x ∆ T+ 0.55 x mc (T2-T0)/4.187
Our condition for water load is as follows:
Room temperature (T0) ... around 20°C
Water load .................................. 1000 g
Heating time .............................. 42 sec.
T2 ............................ Final Temperature
Measuring condition:
1. Container
The water container must be a cylindrical borosilicate glass vessel having a maximum material
thickness of 3 mm and an outside diameter of approximately 190 mm.
2. Temperature of the oven and vessel
The oven and the empty vessel are at ambient temperature prior to the start of the test.
3. Temperature of the water
The initial temperature of the water is (10±1)˚C.
4. Select the initial and final water temperature so that the maximum difference between the final
water temperature and the ambient temperature is 5˚C.
5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.
6. The graduation of the thermometer must be scaled by 0.1˚C at minimum and an accurate
thermometer.
7. The water load must be (1000±5) g.
8. "t" is measured while the microwave generator is operating at full power. Magnetron filament heat-
up time is not included.
NOTE: The operation time of the microwave oven is "t + 3" sec. 3 sec. is magnetron filament heat-
Measuring method:
1. Measure the initial temperature of the water before the water is added to the vessel.
(Example: The initial temperature T1 = 11˚C)
2. Add the 1 litre water to the vessel.
3. Place the load on the centre of the shelf.
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value ∆ T of
10 ˚C.
5. Stir the water to equalize temperature throughout the vessel.
6. Measure the final water temperature. (Example: The final temperature T2 = 21°C)
7. Calculate the microwave power output P in watts from above formula.
TEST PROCEDURES
up time.
COMPONENT TEST
P (W) = 4.187 x V x ∆T / t + 0.55 x mc (T2-T0)/t
Power supply Voltage .............. Rated voltage
Initial temperature (T1) ...................... 10±1°C
Mass of container (mc) ......................... 330 g
P = 100 x ∆T + 0.55 x mc (T2-T0)/42
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