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7

CARRY OUT 3D CHECKS.

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

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 is measured by how much power the water load can absorb. 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.

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 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 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 be 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 + 2” sec. (2 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.
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.

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 .............................. 42 sec.
P = 100 x 

∆

T

8

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

°

C

Temperature after (42 + 2) = 44 sec ......................................................................  T2 = 21

°

C

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

∆

T1 = 10˚C

Measured output power
The equation is “P = 100 x 

∆

T” ................................................ P = 100 x 10

°

C = 1000 Watts

±

CAUTION: 1

°

C CORRESPONDS TO 100 WATTS. REPEAT MEASUREMENT IF THE POWER IS

INSUFFICIENT.

1000g

1000g

1000g

Heat up for 44 sec

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.

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.

CARRY OUT 3D CHECKS.
Disconnect the leads to the primary winding of the high voltage  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 ................................ approximately 1.3 

Ω

b. Secondary winding ............................ approximately 86 

Ω

c. Filament winding .........................................  less than 1 

Ω

If the readings obtained are not stated as above, then the high voltage transformer is probably faulty
and should be replaced.
CARRY OUT 4R CHECKS.

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 10M

Ω

 after

9

CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

Released

Open circuit

Short circuit

Depressed

Short circuit

Open circuit

COM; Common terminal,
NO;

Normally open terminal

NC;

Normally close terminal

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

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a continuity
test across the two terminals as described in the below.

Table: Thermal Cut-out Test

Temperature of "ON"

Temperature of "OFF"

Indication of ohmmeter

Parts Name

 condition  (closed circuit).

condition (open circuit).

(When room temperature

(˚C)

(˚C)

is approx. 20˚C.)

Thermal cut-out 125˚C

This is not resetable type.

Above 125˚C

Closed circuit

Thermal cut-out 145˚C

This is not resetable type.

Above 145˚C

Closed circuit

If incorrect readings are obtained, replace the thermal cut-out.

An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due
to resistricted ventilation, cooling fan failure or a fault condition within the magnetron or HV. circuit.

An open circuit thermal cut-out (OVEN) indicates that the food in the oven cavity may catch fire, this
may be due to over heating produced by improper setting of the cooking timer or failure of the control
panel.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

If the fuse M10A is blown when the door is opened, check the 1st. interlock switch, monitor switch and
monitor resistor.

If the fuse M10A is blown, there could be a short or ground in electrical parts or wire harness. Check
them and replace the defective parts or repair the wire harness.

CARRY OUT 4R CHECKS.

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 10M

Ω

resistance.

F. When the internal wire is opened in the high voltage 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 reading are obtained, the high voltage capacitor must be replaced.

CARRY OUT 4R CHECKS.

10

CARRY OUT 3D CHECKS.

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 219 

Ω

Antenna motor

Approximately 11 k

Ω

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of noise filter.
Using an ohmmeter, check between the terminals as described
in the following table.

Between N and L

Approx. 680 k

Ω

Between terminal N and WHITE

Short circuit

Between terminal L and RED

Short circuit

If incorrect readings are absorbed, replace the noise filter unit.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

If the high voltage fuse is blown, there could be a short in the  high voltage rectifier or the magnetron.
Check them and replace the defective parts and the high voltage fuse.

CARRY OUT 4R CHECKS.

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance can not be performed with only a voltmeter
and ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key
Unit and troubleshooting by replacement is described according to the symptoms indicated.
1.  Key Unit   Note : Check key unit ribbon connection before replacement.

The following symptoms indicate a defective key unit. Replace the key unit.

a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.

2. Control Panel

The following symptoms indicate a defective control unit. Before replacing the control unit.
perform the key unit test (Procedure L) to determine if control unit is faulty.

2-1  In connection with pads

a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.

2-2  In connection with indicators

a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light up.
d) The corresponding segments of all digits do not light up; or they continue to light up.

FUSE
M10A

N

L

DISCHARGE RESISTOR 680 k

Ω

NOISE SUPPRESSION COIL 

LINE BYPASS
CAPACITOR
0.0033

µ

F/ AC 250V

DISCHARGE
RESISTOR 10M

Ω

LINE BYPASS
CAPACITOR
0.0033

µ

F/ AC 250V

LINE CROSS CAPACITOR 0.068

µ

F/ AC 250V

NOISE FILTER