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7

Microwave ovens contain circuitry capable of producing very high voltage and current. Contact with following parts
will result in electrocution.
High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier assembly, High voltage harness.

1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.

WARNING AGAINST THE CHARGE OF THE

HIGH-VOLTAGE CAPACITOR

The high-voltage capacitor remains charged
about 60 seconds after the oven has been
switched off. Wait for 60 seconds and then short-
circuit the connection of the high-voltage capacitor
(that is, of the connecting lead of the high-voltage
rectifier) against the chassis with the use of an
insulated screwdriver.

Sharp recommend that wherever possible fault-finding
is carried out with the supply disconnected. It may in,
some cases, be necessary to connect the supply after
the outer case has been removed, in this event carry out
3D checks and then disconnect the leads to the primary
of the high voltage transformer. Ensure that these leads
remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testing is completed carry out 3D checks and reconnect
the leads to the primary of the high voltage transformer.

When all service work is completed, and the oven is fully assembled, the microwave power output should be checked
and microwave leakage test carried out.

1) Reconnect all leads removed from components

during testing.

2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.

Microwave ovens should not be run empty. To test for
the presence of microwave energy within a cavity, place
a cup of cold water on the oven tray, close the door and
press Manual / Repeat key and set the microwave time
for one (1) minute. Set the power level to 100% and push
the START button. When the one minutes has elapsed
(timer at zero) carefully check that the water is now hot.
If the water remains cold carry out 3D checks and re-
examine the connections to the component being tested.

When troubleshooting the microwave oven, it is helpful to
follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a
specific test be performed. These tests are given a
procedure letter which will be found in the “Test
Procedure”section.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse F2 F6.3A in the 1st latch
switch - monitor switch - monitor resisitor
circuit, check the 1st latch switch, monitor
switch and  monitor resistor before re-
placing the fuse F6.3A

8

CONDITION

“  .  “ does not appear on display when power
cord is plugged into wall outlet.

Control panel can not accept key in.

Fuse F6.3A blows when the door is opened.

Home fuse blowns when power cord is plugged
into wall outlet.

Fuse 13A blowns when power cord is plugged
into wall outlet.

Oven lamp, fan motor and stirrer motors do not
work for 1 minute whenever the door is opened
or after cooking.

Fuse F2 F6.3A blowns when power cord is
plugged into wall outlet.

Oven lamp does not light when door is opened.
(Blower and stirrer motors work)

Blower motor does not work when door is
opened. (Oven lamp  lights and stirrer motors
work)

“EE  1” appear in display.

“EE  2” appear in display.

“EE  3” appear in display .

“EE  6” appear in display.

“EE  7” appear in display.

“EE  9” appear in display.

Oven lamp, blower motor and stirrer motors do
not work.

Oven lamp does not work.

Blower motor does not work.

Oven does not stop after end of cooking cycle or
when STOP/CLEAR key is touched. (Oven lamp,
blower motor and stirrer motors stop.)

Home fuse blows when starting the oven.

Oven goes into cook cycle but shuts down
before end of cooking cycle.

Oven seems to be operating but no heat is
produced in oven load.

It passed more than 1 minute after cooking but
oven lamp, blower motor and stirrer motors do
not stop.

“EE  0” appear in display .

“EE 16” appear in display.

“EE 17” appear in display.

“EE  8” appear in display .

“EE  10” appear in display .

Stirrer motors do not work.

PPROBLEM

TEST PROCEDURE

A

A

B

B

C

C

C

D

D

E

E

E

E

E

F

F

G

H

ON
CONDITION

OFF
CONDITION

MAGNETRON MG1

MAGNETRON MG2

HIGH VOLTAGE TRANSFORMER  T1

HIGH VOLTAGE TRANSFORMER T2

H.V. RECTIFIER ASSEMBLY FOR MG1

H.V. RECTIFIER ASSEMBLY FOR MG2

H.V. WIRE HARNESS

H.V. CAPACITOR C1

H.V. CAPACITOR C2

1ST. LATCH SWITCH

2ND. LATCH SWITCH

3RD. LATCH SWITCH

MONITOR SWITCH

STOP SWITCH

FUSE M8A/ M6.3A F3

FUSE M8A/ M6.3A F4

FUSE 13A

FUSE F6.3A

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

9

MAGNETRON THERMAL CUT-OUT 145˚C TC1

MAGNETRON THERMAL CUT-OUT 145˚C TC2

B. MOTOR THERMAL CUT-OUT 115˚C TC3

OVEN THERMAL CUT-OUTT 115˚C TC4

MONITOR RESISTOR R1

STIRRER MOTOR

MAGNETRON THERMISTOR

EXHAUST THERMISTOR

INTAKE THERMISTOR

OVEN LAMP OR SOCKET

BLOWER MOTOR

NOISE FILTER

POWER SUPPLY CORD

FUSE HOLDER

SHORTED WIRE HARNESS

OPENED WIRE HARNESS

TOUCH CONTROL PANEL

RELAY RY-1, RY-3, RY-4

FOIL PATTERN

BLOCKED VENTILATION OPENINGS

BLOCKED BLOWER MOTOR

MIS ADJUSTMENT OF SWITCHES

HOME FUSE OR BREAKER

NO POWER AT WALL OUTLET

OVER THE MAX. COOKING TIME

DUE TO PROGRAMME LOCK

TEMPERATURE OF EXHAUST THERMISTOR IS HIGH

TEMPERATURE OF INTAKE THERMISTOR IS HIGH

TEMPERATURE OF MAGNETRON THERMISTOR IS HIGH

BLOCKED STIRRER ANTENNA

KEY UNIT

I

I

I

I

J

L

K

K

K

L

M

N

P

Q

O

10

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.

MICROWAVE OUTPUT POWER (IEC-705-1988)
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.

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 (R-2397G) .......... 25 sec.

P=170x

∆

T

Heating time (R-2297G) .......... 35 sec.

P=120x

∆

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 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 can be 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.) Therefore total reheating time = 28 seconds (R-2397G) / 38 seconds (R-2297G).

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.

CARRY OUT 3D CHECK.
Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal.