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R-872M - 12

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.

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 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 the 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 high voltage 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.

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 winding. The following readings should be
obtained:-

a. Primary winding ................................... approximately 2 

Ω

b. Secondary winding ............................ approximately 99 

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 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.

R-872M - 13

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

Above 125˚C

Closed circuit

Thermal cut-out 150˚C

Below 130˚C.

Above 150˚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.

An open circuit thermal cut-out (OVEN) indicates that the oven cavity has overheated, this may be due
to no load operation.

CARRY OUT 4R CHECKS.

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

CARRY OUT 3D CHECKS.
Disconnect theconnector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter.
Connect the ohmmeter leads to Pin No's C1 and C3 of the thermistor harness.

Room Temperature

Resistance

20˚C - 30˚C

Approximately 359.9 k

Ω

 - 152 k

Ω

If the meter does not indiicate above resistance, replace the thermistor.

CARRY OUT 4R CHECKS.

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.

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS.

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately

293 

Ω

Turntable motor

Approximately

15 k

Ω

Convection fan motor

Approximately

288 

Ω

R-872M - 14

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.

CARRY OUT 3D CHECKS.

If the fuse15A is blown, there is a shorts or grounds 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.

1. If the fuse F8A  is blown when the door is opened, check the monitored latch switch and monitor

switch.

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

F8A.

3. If the fuse F8A is blown, there could be shorts in the asymmetric rectifier or there is a ground in wire

harness. A short in the asymmetric rectifier may be occurred due to short or ground in H.V. rectifier,
magnetron, high voltage transformer or H.V. wire. Check them and replace the defective parts or
repair the wire harness.

CARRY OUT 4R CHECKS.

F8A

15A

WHT

RED

R1

R2

N

Cx

Cy

L

L

L

L (min)

Cx 

±

 20%

Cy 

±

 20%

R1

R2

1.0mH

0.22

µ

F

4700pF

10 M

Ω

680k

Ω

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.

Before carrying out the following tests make sure the heating element is cool completely.

1. Resistance of heating element.

Disconnect the wire leads to the heating element to be tested.  Using ohmmeter with low resistance
range. Check the resistance across the terminals of the heating element as described in the
following table.

Table: Resistance of heating element

Parts name

Resistance

Grill heating element (top)

Approximately 61 

Ω

Bottom heating element

Approximately 115 

Ω

2. Insulation resistance.

Disconnect the wire leads to the heating element to be tested. Check the insulation resistance
between the element terminal and cavity using a 500V - 100M

Ω

 insulation tester.  The insulation

resistance should be more than 10 M

Ω

 in the cold start.

If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably
faulty and should be replaced.

CARRY OUT 4R CHECKS.

R-872M - 15

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.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.

2-3  Other possible troubles caused by defective control unit.

a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
d) Proper temperature measurement is not obtained.

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
is making good contact, verify that the door sensing switch (stop switch) operates properly; that is the
contacts are closed when the door is closed and open when the door is open. If the door sensing switch
(stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control unit and
make sure the door sensing switch is closed (either close the door or short the door sensing switch
connecter). Use the Key unit matrix indicated on the control panel schematic and place a jumper wire
between the pins that correspond to the STOP/CLEAR pad making momentary contact. If the control
unit responds by clearing with a beep the key unit is faulty and must be replaced. If the control unit does
not respond, it is faulty and must be replaced.  If a specific pad does not respond, the above method
may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.

CARRY OUT 4R CHECKS.

G 8

G 7

G 6

G 5

G 4

G 3

G 2

G 1

G12

G11

G10

G 9

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 also the Control unit is divided into two units, CPU
unit and Power 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 N) to determine if control unit is faulty.