R-464 (serv.man3). Test procedure - Sharp Home Appliance Service Manual (repair manual)

7

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

CARRY OUT 3D CHECK.

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 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 equip-
ment.
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 1 minute and 33 seconds 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 100.

±

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

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 windings. The following readings should
be obtained:

a. Primary winding .................... approx. 1.3 

Ω

b. Secondary winding ............... approx. 104 

Ω

c. Filament winding ................... less than 1

Ω

If the reading obtained are not stated as above, then the high voltage transformer is probably faulty
and should be replaced.

CARRY OUT 4R CHECKS.

HIGH VOLTAGE RECTIFIER TEST
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 B+C 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 wire is opened in the high voltage 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.

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

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

COM; Common terminal

Released

Open circuit

Short circuit

NO;

Normally open terminal

Depressed

Short circuit

Open circuit

NC;

Normally close terminal

9

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

CARRY OUT 4R CHECKS.

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 table below.

 CARRY OUT 4R CHECKS.

Table: Thermal cut-out Test

Temperature of "ON" condition

Temperature of  "OFF" condition

Indication ofohmmeter

Parts Name

(closed circuit) (˚C)

(open circuit) (˚C)

(When room temperature

 is approx. 20˚C)

Thermal cut-out 125˚C

This is not resetable type.

Above 125˚C

Closed circuit.

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

An open circuit thermal cut-out 125˚C (MG) indicates that the magnetron has overheated, this may
be due to resistricted ventilation, cooling fan failure or a fault condition within the magnetron or HV
circuit.

An open circuit thermal cut-out 125˚C (OVEN) indicates that the foods in the oven may catch fire, this
may  be due to over heating produced by improper setting of the cooking time or failure of the control
panel.

CARRY OUT 3D CHECKS.

Disconnect the leads from the monitor resistor. Using an ohmmeter and set on a low range. Check
between the terminals of the monitor resistor.

The resistance of monitor resistor is approx.  0.8 ohms.

If incorrect readings are obtained, replace the monitor resistor.

 CARRY OUT 4R CHECKS.

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 12 k

Ω

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS

CARRY OUT 3D CHECKS.

1. If the fuse is blown, there could be shorts or ground 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 1st. interlock switch, relay RY1, monitor

switch and monitor resistor.

10

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  high voltage fuse.

CARRY OUT 4R CHECKS.

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

PLACEMENT

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance cannot be performed with only a
voltmeter and ohmmeter. In this service manual, the touch control panel assembly is divided into two
units, Control Unit and Key Unit, and also the Control Unit is divided into two units, CPU Unit and
Power Unit, and troubleshooting by unit replacement is described according to the symptoms
indicated.

1. Key Unit.  Note: Check key unit ribbon connection before replacement.

The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the keys, a certain key produces no signal at all.
b) When touching a number key, two figures or more are displayed.
c) When touching the keys, sometimes a key produces no signal.

2. Control Unit.

The following symptoms indicate a defective control unit. Before replacing the control unit, perform
the Key unit test (Procedure M) to determine if control unit is faulty.

2-1 In connection with keys.

a) When touching the keys, a certain group of keys do not produce a signal.
b) When touching the keys, no keys produce a signal.

2-2  In connection with indicators.

a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.

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

CARRY OUT 4R CHECKS.

CAUTION: ONLY REPLACE FUSE 10A WITH THE CORRECT VALUE REPLACEMENT

CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the noise
filter. Using an ohmmeter, check between the termi-
nals as described in the following table.

MEASURING POINT

INDICATION OF
OHMMETER

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.

NOISE FILTER

RESISTOR 10 M

Ω

 1/2W

FUSE

N

L

LINE CROSS CAPACITOR

0.22

µ

/AC250V 

NOISE SUPPRESSION COIL 

WHT

RED

LINE BYPASS CAPACITOR
0.0033

µ

/AC250V

LINE BYPASS CAPACITOR
0.0033

µ

/AC250V

RESISTOR 680 K

Ω

 1/2W