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R-254M - 9

A

MICROWAVE OUTPUT POWER

The power output of this oven is rated using the method specified by IEC-60705.  Full

details of how to carry out this

procedure can be found in the Sharp Technical Training notes which is available from
Sharp Parts Centre
(part number SERV-LITMW01).

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 IEC-60705 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 2 minutes on full power.

4.

When the 2 minutes 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 5mW/cm

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 the National
Physical  Laboratories are used.

Suitable leakage detectors :

CELTEC A100
APOLLO X1

R-254M - 10

CARRY OUT 3D CHECKS.
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 .......................... 2.2 ohms approximately
b. Secondary winding .................... 140 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.
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, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.

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 10M

Ω

resistance.

F. When the internal  10 M

Ω

 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.

R-254M - 11

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a
continuity test across the two terminals as described in the below.

CARRY OUT 4R CHECKS.

Temperature of "ON" condition  (closed circuit). ................................................... This is not resetable type
Temperature of "OFF" condition (open circuit). ....................................................................... Above 125˚C
Indication of ohmmeter (When room temperature is approx. 20˚C.) ....................................... Closed circuit

If incorrect readings are obtained, replace the thermal cut-out.

An open circuit thermal cut-out (OVEN) indicates that the food in the oven cavity may have caught fire.
This may be due to over heating produced by improper setting of the cooking timer or failure of the
control panel.

CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals
as described in the following table.

COM; Common terminal,
NO;

Normally open terminal

NC;

Normally close terminal

If incorrect readings are obtained, replace the switch.

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

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 and monitor switch.

If the fuse is blown by incorrect door switching replace the defective switch(es) and the  fuse F1.
If the fuse is blown by incorrect door latch setting, adjust latch hook until all switches close when
door is shut.
Ensure door, latches and cavity face plate are flat.
Ensure switches are firmly fixed in latch hook.

CARRY OUT 4R CHECKS.

R-254M - 12

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 360 

Ω

Turntable motor

Approximately 12 - 15 k

Ω

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads

remain isolated from other oven components and chassis (Use insulation tape if necessary.)

3. Connect the voltmeter, set to 250V AC, across the motor terminals. (Refer to the relevant motor test

procedure or pictorial diagram for the correct terminal numbers.)

4. Arrange the meter in a position where it can be read during the test.

(Do not touch the meter, meter leads or oven circuitry while the oven is active.)

5. Close the oven door.
6. Set  the power level to HIGH and set the relevant timer for about three (3) minutes.
7. Note the reading on the meter and carefully observe the motor under test to see if it is turning.
8. CARRY OUT 3D CHECKS.
9. Remove the test meter leads.
10.Reconnect the leads to the primary of the high voltage transformer.

If a reading of the line voltage was obtained (step 7) but the motor was not turning then it is faulty and
should be replaced. If the meter indicated that the no supply was present then the winding to the motor
should be checked for resistance.

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

Approx. 680 k

Ω

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.

F: FUSE

    F1

N

L

0.22

µ

/AC250V 

680K/ 0.5W 

10M/ 0.5W 

NOISE 
SUPPRESSION COIL 

0.0033

µ

/ 250V

0.0033

µ

/ 250V

NOISE FILTER

RED

WHT

CARRY OUT 3D CHECKS.