R-234 (serv.man2). Part 1 Text (1-28) - Sharp Home Appliance Service Manual (repair manual). Page 12

R-234 - 12

CARRY OUT 3D CHECK

Isolate the magnetron from high voltage circuit by removing all leads connected to the filament terminal.

To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.

To test for a short circuit filament to anode condition, connect ohmmeter between one of the filament
terminals and the case of the magnetron (ground). This test should be indicated an infinite resistance.
If a low or zero resistance reading is obtained then the magnetron should be replaced.

condition (outer case fitted). Microwave output power from the magnetron can be measured by way of
IEC 60705.  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

P (W) = 4.187 x V x 

∆

T / t

Our condition for water load is as follows:
Room temperature..............around 20

°

C

Power supply Voltage.........Rated voltage

Water load.........1000 g

Initial temperature...........10 

±

 2

°

C

Heating time....52 + 3 = 55 sec.

P = 80 x 

∆

T

The following test procedure should be carried out with the microwave oven in a fully assembled

NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE
THE OVEN IS IN OPERATION.

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 

±

 2)

°

C.

4. Select the initial and final water temperature so that the maximum difference between the final water

temperature and the ambient temperature is 5K.

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 seconds are needed for magnetron

filament heat-up time.

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 

±

 2) K.

5. Stir the water to equalize temperature throughout the vessel.