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7

cavity, the oven temperature fuse will open at 120˚C,
causing the oven to shut down. The defective temperature
fuse must be replaced with new rated one.

This temperature fuse TF3 protects the blower motor
against overheating. If its temperature goes above 120˚C
because the blower motor is stalled or the ventilation
openings 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 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 stirrer motors SM drive stirrer anten-
nas 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.

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 SW1 - monitor

switch SW4 - monitor resisitor R1 circuit, check the 1st latch switch SW1, monitor switch SW4 and  monitor
resistor  R1 before replacing the fuse F2 F6.3A

8

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

wall outlet.

Control panel can not accept key in.

Fuse F2 F6.3A blows when the door is opened. 

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

Fuse F1 F13A 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 F2 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 MG1 failure) 

“EE  2” (Magnetron MG2 failure)

“EE  3” (Magnetron MG1 and MG2 failure) 

“EE  6” (Thermistor (1) failure)  

“EE  7” (Exhaust air temperature is high) 

“EE  9” (Exceeded max. heating time) for R-22AT/ R-24AT

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. and (2) are open.) 

“EE 17” (Magnetron temperature is high.) 

“EE  8” (Relay melt short)

Stirrer motors do not work.

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 SW1 

2ND. LATCH SWITCH SW2 

3RD. LATCH SWITCH SW3

MONITOR SWITCH SW4 

STOP SWITCH SW5

FUSE M8A F3

FUSE M8A F4

FUSE F13A F1

FUSE F6.3A F2

MAGNETRON TEMPERATURE FUSE TF1

MAGNETRON TEMPERATURE FUSE TF2

B. MOTOR TEMPERATURE FUSE TF3

OVEN TEMPERATURE FUSE TF4

MONITOR RESISTOR R1

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 [for R-22AT/24AT], RY2 [for R-23AM]

RELAY RY-4 [for R-22AT/24AT], RY3 [for R-23AM]

FOIL PATTERN

Mis adjustment of switches

HOME FUSE or BREAKER

No power at wall outlet

Over the max. cooking time [for R-22AT/24AT]

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 [for R-22AT/24AT], or SWITCH UNIT [for R-23AM]

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

CONDITION

OFF

CONDITION

ON

CONDITION

PROBLEM

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-23AM/24AT]

Mass of container (mc) ..... 330 g

T2 ......... Final Temperature

P = 150 x 

∆

T [R-22AT] / P = 190 x 

∆

T [R-23AM, 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-23AM/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-23AM/24AT] ................ P = 190 x 10

°

C = 1900 Watts

±

CAUTION: 1

°

C CORRESPONDS TO 150 WATTS [R-22AT]/ 190 WATTS [R-23AM, R-24AT]. REPEAT

MEASUREMENT IF THE POWER IS INSUFFICIENT.

1000g

1000g

1000g

Heat up for 31 sec. for R-22AT

Heat up for 25 sec. for R-23AM/ R-24AT

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-23AM,

R-24AT]  on fill power.

4. When the  56 sec. [R-22AT]/ 44 sec. [R-23AM, 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-23AM, 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