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R-291(K)M

6 – 1

R218L(W)

The door is opened by pushing the open button on the control panel,
refer to the Figure D-1.

When the open button is pushed, the open button pushes up the
switch lever, and then the switch lever pushes up the latch head. The
latch heads are moved upward and released from latch hook. Now the
door will open.

1. When the oven door is closed, the contacts (COM-NO) must be

closed.

1. When the oven door is closed, the contacts (COM-NC) must be

opened.

2. When the oven door is opened, the contacts (COM-NC) must be

closed.

3. If the oven door is opened and the contacts (COM-NO) of the mon-

itored latch switch, the contacts of the relay RY1 and the timer
switch fail to open, the fuse T6.3A blows immediately after closing
the contacts (COM-NC) of the monitor switch.

CAUTION: BEFORE REPLACING A BLOWN FUSE TEST THE MON-

ITORED LATCH SWITCH, RELAY RY1, TIMER SWITCH
AND MONITOR SWITCH FOR PROPER OPERATION.
(REFER TO CHAPTER “TEST PROCEDURE”.)

1. The fuse T6.3A blows when the contacts (COM-NO) of the moni-

tored latch switch, the contacts of the relay RY1 and the timer
switch remain closed with the oven door open and when the con-
tacts (COM-NC) of the monitor switch are close.

2. If the wire harness or electrical components are short-circuited, the

netron is shorted.

The temperature fuse located on the  top of the oven cavity is designed

by either error in cook time or defect in the control unit, the tempera-
ture fuse will open. Under normal operation, the temperature fuse
remains closed. However, when abnormally high temperatures are
reached within the oven cavity, the temperature fuse will open at
150 C, causing the oven to shut down. The defective temperature fuse
must be replaced with a new one.

The turntable motor drives the turntable roller assembly to rotate the
turntable.

The fan motor drives a blade which draws external cool air. This cool

This sensor detects the humidity from the food which is being cooked,

The noise filter prevents the radio frequency interference that might
flow back in the power circuit.

to control its automatic cooking.

air is directed through the air vanes surrounding the magnetron and
cools the magnetron. This air is channelled through the oven cavity to

exhausted through the exhausting  air vents at the oven cavity.

Figure D-1. Door Open Mechanism

Latch Heads

Latch Hook

Door

Door Sensing Switch

Secondary Interlock Switch

Monitor Switch

R-291(K)M

7 – 1

R218L(W)

When troubleshooting the microwave oven, it is helpful to follow the
Sequence of Operation in performing  the checks. Many of the possible

tests are given a procedure letter which will be found in the “Test Pro-
cedure” section.

IMPORTANT:

If the oven becomes inoper ative because of a blown fuse T6.3A in the
monitored latch switch - relay RY1 - timer switch - monitor switch cir-
cuit, check the monitored latch switch, relay RY1, timer switch and
monitor switch before replacing the fuse T6.3A.

HUMIDITY SENSOR

NOISE FILTER

SENSOR
COOKING
CONDITION

Humidity sensor does not end
during Sensor cooking condition.
(Oven doesnot shut off after a
cup of water is boiling by sen-
sor cooking.)

Oven stops at 16 sec. after
starting.

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SECONDARY INTERLOCK SWITCH

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OFF
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PROBLEM

CONDITION

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

TEST PROCEDURE

ON
CONDITION

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RE CK CK RE CK CK CK CK CK

Home fuse blows when power

supply cord is plugged into

wall outlet.
FUSE T6.3A blows when

power supply cord is plug-

ged into wall outlet.

"88:88" does not appear in
display but power supply cord
is plugged into wall outlet.
Display does not operate

properly when STOP/CLEAR

pad is touched.
Oven does not start when

the START pad is touched.

(Display appears)
Oven lamp does not light

(Display appears.)
Fan motor does not operate.

(Display appears.)
Turntable motor does not

operate. (Display appears.)
Oven or any electrical parts

does not stop when cooking

time is 0 or STOP/CLEAR

pad is touched.
Oven seems to be operating

but little or no heat is pro-

duced in oven load. (Micro-

wave power level is set at

HIGH)
Oven does not seems to be

operating

properly

when

70%,50%, 30% or 10% is

set. (Oven operates properly

at 100%.)
Oven goes into cook cycle

but shuts down before end

of cooking cycle.

R-291(K)M

8 – 1

R218L(W)

CARRY OUT 3D CHECKS.

r should show a

reading of less than 1 ohm.

he magnetron

on should be replaced.

icrowave output power

from the magnetron can be measured by IEC test procedure, 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(sec-

ond), 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 hav ing 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 1) C

t 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 an accurate thermometer.

7) The water load must be (1000 5) g.

NOTE

Measuring method:

1) 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 100% for the temperature of the water rises by a value  T of 10 C.

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

C)

7) Calculate the microwave power output P in watts from above formula.

CAUTION: 1 C CORRESPONDS TO 80 WATTS. REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.

   The formula is as follows;

           P x t / 4.187 = V x   T+ 0.55 x mc (T2-T0)/4.187                     P (W) = 4.187 x V x  T / t + 0.55 x mc (T2-T0)/t
   Our condition for water load is as follows:
          Room temperature (T0) ......................... around 20°C                          Power supply ........................... VoltageRated voltage
          Water load ...............................................................1000 g                          Initial temperature (T1) .................................... 10±1°C
          Heating time .......................................................... 52 sec.                          Mass of container (mc) ...................................... 330 g

          T2 ........................................................ Final Temperature                T = T2 - T1                 P = 80 x  T + 0.55 x mc (T2-T0)/52

          Room temperature ................................................................... To = 21 C
          Initial temperature ..................................................................... T1 = 11 C
          Temperature after (52 + 3) = 55 sec ...................................... T2 = 21 C

C

          Measured output power

          The equation is "P = 80 x  T" .................... P = 80 x 10 C = 800 Watts

R-291(K)M

8 – 2

1. CARRY OUT 3D CHECKS.

nections 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 -------------------- 2.8 ohms approximately

                  b.Secondary winding --------------- 204 ohms approximately 

                  c.Filament winding ------------------------------ less than 1 ohm

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

3. Also, the high voltage transformer has the thermal cut-out in  the primary coil. The thermal cut-out will open when the temperature of the thermal

cut-out in the primary coil reaches approximately 150 C. The thermal cut-out resets automatically at 130 C. If an ohmmeter indicates an open cir-
cuit under normal condition, replace the high voltage transformer because the primary coil (thermal cut-out) has opened. An open primary coil

former, especially the

ventilation opening.

4. CARRY OUT 4R  CHECKS.

CARRY OUT 3D CHECKS.

o its highest range.

d note this second

 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 DIRECTION.

CARRY OUT 3D CHECKS.

1. Isolate the high voltage capacitor from the circuit.

2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.

3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M  after it has been charged.

4. A short-circuited capacitor shows continuity all the time.

5. An open capacitor constantly shows a resistance about 10 M  because of its internal 10M  resistance.

If incorrect reading 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.

WARNING:

Table: Terminal Connection of Switch

Plunger Operation                    COM to NO            COM to NC                          COM; Common terminal
Released                                       Open circuit          Short circuit 

NO;     Normally open terminal 

Depressed                                    Short circuit          Open circuit.

NC;     Normally close terminal

1000g

1000g

1000g