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R-61FBSTM/R-62FBSTM - 9

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 turntable.
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.

R-61FBSTM/R-62FBSTM - 10

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 (52+ 3) = 55 sec. .............................................................................  T2 = 21

°

C

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

∆

T1 = 10

°

C

Measured output power
The equation is “P = 80 x 

∆

T” ............................................................... P = 80 x 10

°

C = 800Watts

±

CAUTION: 1

°

C CORRESPONDS TO 80  WATTS. REPEAT MEASUREMENT IF THE POWER IS

INSUFFICIENT.

Heat up for 55 sec.

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 ............ 2 ohms approximately
b. Secondary winding ....... 160 ohms approximately
c. Filament winding ........... less than 1 ohm

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

CARRY OUT 4R CHECKS

1000g

1000g

1000g

R-61FBSTM/R-62FBSTM - 11

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, replace the switch.

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 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 reading are obtained, the high voltage capacitor must be replaced.

CARRY OUT 4R CHECKS

D2

D1

ASYMMETRIC
RECTIFIER

HIGH VOLTAGE 
RECTIFIER

A

B

C

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.

Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested
using an ohmmeter set to its highest range 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 direction 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 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 OF AT LEAST 6 VOLTS,
BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH
DIRECTIONS.

CARRY OUT 4R CHECKS

ASYMMETRIC RECTIFIER TEST

CARRY OUT 3D CHECKS.

R-61FBSTM/R-62FBSTM - 12

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.

CARRY OUT 4R CHECKS

Table: Thermal Cut-out Test

Temperature of

Temperature of

Indication of

"ON" condition

"OFF" condition

ohmmeter

Parts Name

(closed circuit).

(open circuit).

(When room

(˚C)

(˚C)

temperature is
approx. 20˚C.)

Thermal cut-out

Below 115˚C

Above 145˚C

Closed circuit

145˚C TC01

Thermal cut-out

This is not resetable

 Above 125˚C

Closed circuit

125˚C TC02

type

If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (MG)  TC02 indicates that the magnetron has overheated, this may be
due to resistricted ventilation, cooling fan failure.
An open circuit thermal cut-out (OVEN) TC01 indicates that the oven cavity has overheated, this may
be due to no load operation.

CARRY OUT 3D CHECKS.
If the fuse 20A is blown, there could be a shorts or a ground in electrical parts or wire harness. Check
them and replace the defective parts or repair the wire harness.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.
If the fuse F8A  (F2) is blown when the door is opened, check the primary latch switch, monitor switch
and monitor resistor.

If the fuse F8A  (F2) is blown by incorrect door switching replace the defective switch(es) and the  fuse
F8A  (F2).

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS

Disconnect the leads from the terminals of
noise filter.
Using an ohmmeter, check between the ter-
minals 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

L (min)

Cx 

±

 20%

Cy 

±

 20%

1.0mH

0.22

µ

F

4700pF

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

CARRY OUT 4R CHECKS

RED

WHT

L

L

R1

L

R2

N

Cx

Cy

R1: 10M ohm  ± 20%
R2: 680k ohm  ± 20%

F8A

20A