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7

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.

The thermistor is a negative temperature coefficient type.
The air temperature around the magnetron is detected
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 magnetron thermistor is open, the control panel will
display "EE16" and the oven will stop.
If the magnetron thermistor is short, the control panel will
display "EE19" and the oven will stop.

The blower motor BM 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 antenna motors SM drive stirrer
antennas.

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 condition.

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 F1 F10A (or F2 F10A) in the interlock switch

SW1 (or SW2) - monitor switches SW3 (or SW4) , check the interlock switch SW1 (or SW2) and monitor
switches SW3 (or SW4) before replacing the fuse F1 F10A (or F2 F10A).

8

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

wall outlet.

Control panel can not accept key in.

Fuse F1 or F2 blows when the door is opened. 

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

Weak point F3 blows when power cord is plugged into wall outlet.

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

minute when the door is opened or after cooking.

Fuse F1 or F2 blows when power cord is plugged into wall outlet. 

Oven lamp does not light when door is opened. (Blower and antenna 

motors work)

Blower motor does not work when door is opened. (Oven lamp  

lights and antenna motors work)

“EE  1” (Magnetron MG1 failure) 

“EE  2” (Magnetron MG2 failure)

“EE  3” (Magnetron MG1 and MG2 failure) 

“EE  6” (Exhaust thermistoropen)  

“EE  7” (Exhaust air temperature is high) 

“EE  9” (Exceeded max. heating time) 

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

Oven lamp does not work. 

Blower motor does not work. 

Oven does not stop after end of cooking cycle. 

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 magnetron are open.) 

“EE 17” (Magnetron temperature is high.) 

“EE  19” (Magnetron thermistor short)

“EE  10” (Fault of memory)

Antenna motors do not work.

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

CONDITION

OFF

CONDITION

ON

CONDITION

PROBLEM

EEP ROM  I-2

N

KEY UNIT
TOUCH CONTROL TRANSFORMER T3
Due to programme lock
Over the max. cooking time 
No power at wall outlet
HOME FUSE or BREAKER
Mis adjustment of switches

P

FUSE 2.5A

O

RELAY RY-4

O

RELAY RY-3

O

RELAY RY-1

M

TOUCH CONTROL PANEL
Opened wire harness
Shorted wire harness
POWER SUPPLY CORD

K

NOISE FILTER
OVEN LAMP OR SOCKET

J

BLOWER MOTOR BM

J

ANTENNA MOTORS SM

I

EXHAUST THERMISTOR TH3

I

MAGNETRON THERMISTOR (Lower) TH2

I

MAGNETRON THERMISTOR (Upper) TH1

L

HIGH VOLTAGE FUSE F5

L

HIGH VOLTAGE FUSE F4

H

EXHAUST TEMPERATURE FUSE TF3

H

MAGNETRON TEMPERATURE FUSE TF2

H

MAGNETRON TEMPERATURE FUSE TF1

F

WEAK POINT F3

G

FUSE F10A F2

G

FUSE F10A F1

E

STOP SWITCH SW5

E

MONITOR SWITCH SW4 

E

MONITOR SWITCH SW3

E

NTERLOCK SWITCH SW2 

D

INTERLOCK SWITCH SW1 

D

H.V. CAPACITOR C2

D

H.V. CAPACITOR C1
H.V. WIRE HARNESS

C

H.V. RECTIFIER ASSEMBLY FOR MG2

C

H.V. RECTIFIER ASSEMBLY FOR MG1

B

HIGH VOLTAGE TRANSFORMER T2 (Rear)

B

HIGH VOLTAGE TRANSFORMER  T1 (Front)

A

MAGNETRON MG2 (Lower)

A

MAGNETRON MG1 (Upper)

9

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 way
of IEC 60705, 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. [R-22AT] / 22sec. [R-24AT]

Mass of container (mc) ..... 330 g

T2 ......... Final Temperature

P = 150 x 

∆T [R-22AT] / P = 190 x ∆T [R-24AT]

10

Room temperature .................................................................................................  T0 = 21

°C

Initial temperature ..................................................................................................  T1 = 11

°C

Temperature after (28 + 3) = 31 sec [for R-22AT] ..................................................  T2 = 21

°C

Temperature after (22 + 3) = 25 sec [for R-24AT] ..................................................  T2 = 21

°C

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

∆T1 = 10˚C

Measured output power
The equation is “P = 150 x 

∆T”  [for R-22AT] ........................... P = 150 x 10°C = 1500 Watts

The equation is “P = 190 x 

∆T”  [for R-24AT] ........................... P = 190 x 10°C = 1900 Watts

Heat up for 31 sec. for R-22AT
Heat up for 25 sec. for R-24AT

1000g

1000g

1000g

±

CAUTION: 1

°C CORRESPONDS TO 150 WATTS [R-22AT]/ 190 WATTS [R-24AT]. REPEAT

MEASUREMENT IF THE POWER IS INSUFFICIENT.

The power output of this oven is rated using the method specified by  IEC 60705. Full details of how
to curry out this procedure can be found in the Sharp Technical Training notes which is available from
Sharp Parts Centre (part number SERV-LITMW01).

The IEC-60705 procedure must be carried out using laboratory-type procedures and equipment.
These requirements make the procedure unsuitable for routine performance checks.

NOTE: The following test method gives an indication of the output power only, it cannot be used to

establish the actual/rated output power. If the true output power is required, then the IEC60705
test method must be used.

Alternative simplified method:
1. Place 2  litres of cold water (between 12

°C and 20°C) in a suitable container.

2. Stir the water and measure the temperature in 

°C. Note temperature as T1.

3. Place the container in the microwave and heat the water for  56 sec. [R-22AT]/ 44 sec. [R-24AT]  on

fill power.

4. When the  56 sec. [R-22AT]/ 44 sec. [R-24AT]   is completed, remove the  container and stir the water.

Note temperature as T2.

5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 150 for R-22AT.
R.F. Power Output = (T2 - T1) x 190 for R-24AT.

±

MICROWAVE LEAKAGE TEST
This oven should be tested for microwave leakage on completion of any repair or adjustment, following
the procedure described in the Sharp Technical Training notes (part number SERV-LITMW01). The
maximum leakage permitted in BS EN 60335-2-25 is 50W/m

2 

(equivalent to 5W/m

2

), however it is not

normal to detect any significant leakage, therefore, any leakage which is detected should be
investigated.

It is essential that only leakage detectors with current calibration traceable to National Physical
Laboratories are used.

Suitable leakage detectors: CELTEC A100

APOLLO X1