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R-334 - 13

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R-334 - 14

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 sec. is 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.

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

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...........46.5 sec.

P = 90 x 

∆

T

CARRY OUT 3D CHECK

Isolate the magnetron from the 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.

MICROWAVE OUTPUT POWER (IEC-60705)
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 way of
IEC 705, 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.

R-334 - 15

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.

Initial temperature .........................................................................................................  T1 = 11

°

C

Temperature after (46.5 + 3) = 49.5 sec. ......................................................................  T2 = 21

°

C

Temperature difference Cold-Warm ............................................................................  

∆

T1 = 10

°

C

Measured output power
The equation is “P = 90 x 

∆

T” .............................................................. P = 90 x 10

°

C = 900 Watts

±

CAUTION: 1

°

C CORRESPONDS TO 90 WATTS. REPEAT MEASUREMENT IF THE POWER IS

INSUFFICIENT.

CARRY OUT 3D CHECKS

Disconnect the leads to the primary winding of the power transformer.  Disconnect the filament and
secondary winding connections from the rest of the HV circuitry. Using an ohmmeter,  set on a low range,
it is possible to check the continuity of all three windings. The following readings should be obtained:-

a. Primary winding ............ 1.9 ohms approximately
b. Secondary winding ....... 120 ohms approximately
c. Filament winding ........... less than 1 ohm

If the reading obtained are not stated above, then the power transformer is probably faulty and should
be replaced.

CARRY OUT 4R CHECKS

HIGH VOLTAGE RECTIFIER TEST

CARRY OUT 3D CHECKS.

Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier  can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B + C of the high
voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading.
The normal resistance is infinite in one direction and more than 100 k

Ω

 in the other direction.

Heat up for 49.5 sec.

1000g

1000g

1000g

R-334 - 16

CARRY OUT 3D CHECKS

A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out  with measuring instrument which is set to the highest resistance

range.

C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10 M

Ω

 after

it has been charged.

D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 M

Ω

 because of its internal 10 M

Ω

resistance.

F. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite

resistance.

G. The resistance across all the terminals and the chassis must be infinite when the capacitor is  normal.
        If incorrect readings are obtained, the high voltage capacitor must be replaced.

CARRY OUT 4R CHECKS

CARRY OUT 3D CHECKS

Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the
following table.

COM;

Common terminal

NO;

Normally open terminal

NC;

Normally close terminal

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

Released

Open circuit

Short circuit

Depressed

Short circuit

Open  Circuit

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.

CARRY OUT 4R CHECKS.

CARRY OUT 4R CHECKS

ASYMMETRIC RECTIFIER TEST

CARRY OUT 3D CHECKS.

Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminals A + B of the
asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second
reading. If an open circuit is indicated in both directions then the asymmetric rectifier is good. If an
asymmetric rectifier is shorted in either direction, then the asymmetric rectifier is probably faulty and must
be replaced with the high voltage rectifier. When the asymmetric rectifier is defective, check whether
magnetron, high voltage rectifier, high voltage wire or filament winding of the power transformer is
shorted.

CARRY OUT 4R CHECKS

NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF

THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.