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7

NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED
TOOL WHILE THE OVEN IS IN OPERATION.

1.

CARRY OUT 3D CHECKS.

2. To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity

check across the magnetron filament leads should indicate less than 1 ohm.

3. To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament

leads and chassis ground. This test should indicate an infinite resistance. If there is little or no
resistance the magnetron is grounded and must be replaced.

4. Reconnect all leads removed from components during testing.
5. Reinstall the outer case (cabinet).
6. Reconnect the power supply cord after the outer case is installed.
7. Run the oven and check all functions.

MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (outer case fitted).
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 IEC60705 procedure must be carried out using laboratory-type procedures and
equipment.
These requirements make the procedure unsuitable for routine performance checks.

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 1 minute and 48 seconds on full

power.

4. When the 1 minute and 48 seconds is completed, remove the  container and stir the water. Note

the water temperature as T2.

5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 80.

±

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

8

1.

CARRY OUT 3D CHECKS.

2. Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the

filament and secondary winding connections 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 .......................... 3.3 ohms approximately
b. Secondary winding .................... 207 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. Measure the resistance

of the primary coil. The resistance of the primary coil should be above resistance unless 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 circuit under normal condition,
replace the high voltage transformer because the primary coil (thermal cut-out) has opened. An open
primary coil (thermal cut-out) indicates overheating of the high voltage transformer. Check for
restricted air flow to the high voltage transformer, especially the ventilation opening.

4. CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier  can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal of the high
voltage rectifier and note the reading obtained. Reverse the meter leads and note this second
reading.
The normal resistance is infinite in one direction and more than 100 k

Ω 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, BE-
CAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIREC-
TIONS.

CARRY OUT 3D CHECKS.

A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest

resistance range.

C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M

Ω

after it has been charged.

D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 M

Ω because of its internal 10MΩ

resistance.

F. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite

resistance.

G. The resistance across all the terminals and the chassis must be infinite when the capacitor is

normal.

If incorrect reading are obtained, the high voltage capacitor must be replaced.

CARRY OUT 4R CHECKS.

9

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of noise filter.
Using an ohmmeter, check between the terminals as described in
the following table.

Between N and L

Open circuit

Between terminal N and WHITE

Short circuit

Between terminal L and RED

Short circuit

If incorrect readings are obtained, replace the noise filter unit.

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.

CARRY OUT 3D CHECKS.

A continuity check across the temperature fuse terminals should indicate a closed circuit unless the
temperature of the temperature fuse reaches approximately 248˚F(120˚C).

An open temperature fuse indicates overheating of the oven, exchange the temperature fuse and
check inside of oven cavity and for improper setting of cooking time or operation of control unit. Check
for restricted air flow through the vent holes of the oven cavity, especially the cooling fan and air guide.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

1. If the fuse  is blown, there could be a shorts or grounds in electrical parts or wire harness. Check

them and replace the defective parts or repair the wire harness.

2. If the fuse is blown when the door is opened, check the monitored latch switch, monitor switch,

timer switch and relay RY1.

If the fuse is blown by incorrect door switching replace the defective switch(es) and the  fuse.

CARRY OUT 4R CHECKS.

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

Released

Open circuit

Short circuit

Depressed

Short circuit

Open circuit

COM; Common terminal,
NO;

Normally open terminal

NC;

Normally close terminal

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.

CARRY OUT 4R CHECKS.

FUSE
T6.3A

N

L

LINE CROSS CAPACITOR

0.068

µ/AC250V 

NOISE SUPPRESSION COIL 

LINE BYPASS
CAPACITOR
0.0022

µ/AC250V

LINE BYPASS
CAPACITOR
0.0022

µ/AC250V

NOISE FILTER

WHT

RED

10

CARRY OUT 3D CHECKS.

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 400 

Ω

Turntable motor

Approximately 14.5 k

Ω

If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.
If the high voltage fuse is blown, there could be a short in the high voltage rectifier or the magnetron.
Check them and replace the defective parts and the high voltage fuse.

CARRY OUT 4R CHECKS.

CAUTION: ONLY REPLACE HIGH VOLTAGE FUSE WITH THE CORRECT VALUE REPLACE-

MENT.

CARRY OUT 3D CHECKS before any of the following timer tests.

TIMER SWITCH- CONTACTS
Disconnect the leads from terminals described at following table. Connect an ohmmeter across
terminals described at following table.
Advance the timer and check that a short circuit reading is obtained on the meter.
Turn the timer back to the zero (0) position and check that an open circuit reading is obtained on the
meter. If these readings are not obtained then replace the timer.

Disconnecting and checking terminals

1 and 2

TIMER - MOTOR
Disconnect the leads from terminals described at following table. Connect an ohmmeter across the
timer motor winding, terminals are described at following table, and check that a reading of resistance
described at following table is indicated.
If this reading is not obtained then the timer is probably defective and should be replaced.

Disconnecting and checking terminals

3 and 4

Resistance of motor winding

approximately 22.2 kohms

CARRY OUT 4R CHECKS after any of the above tests.

 CAUTION: DO NOT TOUCH THE ELECTRICAL PARTS AND THE PRINTED WIRING BOARD

TO PREVENT AN ELECTRIC  SHOCK. BECAUSE THE CONTROL UNIT IS “
TRANSLESS CIRCUIT ” AND ALL ELECTRICAL PARTS  ARE USED AT A.C. LINE
VOLTAGE.

The control unit consists of circuits including semiconductors such as LSI, etc. Therefore, unlike
conventional microwave ovens, proper maintenance can not be performed with only a voltmeter and
ohmmeter.

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2

3

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