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7

This temperature fuse protects the blower motor against
overheating. If its temperature goes above 120˚C be-
cause the blower motor is stalled or the ventilation open-
ings are blocked, the contacts of the temperature fuse will
open. The line voltage to the control unit will be cut off and
the operation of the oven will be stopped. The defective
temperature fuse must be replaced with a new one.

The thermistor is a negative temperature coefficient type.
The temperature in the exhaust duct is detected through
the resistance of the thermistor.
If the temperature is high, the control panel will display
“EE7” and the oven will stop to avoid overheating and
catching fire.
If the thermistor is open, the control panel will display
"EE6" and the oven will stop.

This thermistor detects temperature of the oven cavity
bottom plate. The thermistor is a negative temperature
coefficient type. The temperature is detected through the
resistance of the thermistor.
If the temperature is high, the control will display “EE17”
and the oven will stop.

The thermistor is a negative temperature coefficient type.
The air temperature around the upper magnetron is de-
tected through the resistance of the thermistor.
If the temperature is high, the control panel will display
"EE17" and the oven will stop to protect the lower magn-
etron against overheat.
If the oven thermistor (2) and the magnetron thermistor are
open at the same time, the control panel will display
"EE16" and the oven will stop.

The blower motor drives a blade which draws external cool
air into the oven. This cool air is directed through the air
vanes surrounding the magnetrons and cools the
magnetrons. This air is channelled through the oven cavity
to remove steam and vapours given off from the heating
foods. It is then exhausted through the exhausting air
vents at the oven cavity.

The upper and lower stirrer motors drive stirrer antennas
to stir the microwave radiation from the upper and lower
waveguides.

The oven cavity light illuminates the interior of the oven so
that food being cooked can be examined visually through
the door window without having to open the door. The
oven lamp is on during the cooking cycle and idle condi-
tion.

8

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 proce-
dure letter which will be found in the “Test Procedure”
section.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse F6.3A in the 1st. latch
switch - monitor switch - monitor resistor
circuit, check the 1st. latch switch, monitor
switch and  monitor resistor before replac-
ing the fuse F6.3A.

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 con-
nection 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 should be carried out.

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 fuse, High
voltage harness.

1) Reconnect all leads removed from components dur-

ing 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 turntable, close the door
and set the power level to HIGH (100%) and set the
microwave timer for two (2) minutes. And push the start
key. When the two 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.

9

“  .  “ 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 blows when power cord is plugged into wall outlet. 

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

Oven lamp, fan motor and stirrer motors do not work for 1 minute 

when the door is opened or after cooking.

Fuse F6.3A blows 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” (Magnetron (1) failure) 

“EE  2” (Magnetron (2) failure)

“EE  3” (Magnetron (1) and (2) failure) 

“EE  6” (Thermistor (1) failure)  

“EE  7” (Exhaust air temperature is high) 

“EE  9” (Exceeded max. heating time) 

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. (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. 

It passed more than 1 minute after cooking but oven lamp, blower 

motor and stirrer motors do not stop.

“EE 16” (Thermistor of MG. (1) and (2) are open.) 

“EE 17” (Magnetron temperature is high.) 

“EE  8” (Relay melt short)

Stirrer motors do not work.

MAGNETRON (1)

MAGNETRON (2)

HIGH VOLTAGE TRANSFORMER (1)

HIGH VOLTAGE TRANSFORMER (2)

H.V. RECTIFIER ASSEMBLY FOR MAG. (1)

H.V. RECTIFIER ASSEMBLY FOR MAG. (2)

H.V. WIRE HARNESS

H.V. CAPACITOR (1)

H.V. CAPACITOR (2)

1ST. LATCH SWITCH 

2ND. LATCH SWITCH 

3RD. LATCH SWITCH

MONITOR SWITCH 

STOP SWITCH

FUSE M8A (1)

FUSE M8A (2)

FUSE F13A

FUSE F6.3A

MAGNETRON (1) TEMPERATURE FUSE

MAGNETRON (2) TEMPERATURE FUSE 

B. MOTOR TEMPERATURE FUSE  

OVEN TEMPERATURE FUSE 

MONITOR RESISTOR 

MAGNETRON THERMISTOR

OVEN THERMISTOR (1)

OVEN THERMISTOR (2)

STIRRER MOTORS SM

BLOWER MOTOR BM

HIGH VOLTAGE FUSE(S)

OVEN LAMP OR SOCKET

NOISE FILTER

POWER SUPPLY CORD

FUSE HOLDERS

Shorted wire harness

Opened wire harness

TOUCH CONTROL PANEL

RELAY RY-1

RELAY RY-3 

RELAY RY-4

FOIL PATTERN

Mis adjustment of switches

HOME FUSE or BREAKER

No power at wall outlet

Over the max. cooking time

Due to programme lock

Temperature of magnetron thermistor is high.

Temperature of oven thermistor (1) is high.

Temperature of oven thermistor (2) is high.

KEY UNIT 

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

CONDITION

OFF

CONDITION

ON

CONDITION

PROBLEM

10

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 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.

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 IEC
test procedure, 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

±

1)

°

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 + 3” sec. (3 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 until 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+ 0.55 x mc (T2-T0)

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 Voltage .............. Rated voltage

Water load ..................................... 1000 g

Initial temperature (T1) ...................... 10

±

1

°

C

Heating time .................................. 28 sec.

Mass of container (mc)............................ 330 g

T2 ............................... Final Temperature

P = 150 x 

∆

T