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R353M - 5

1.  When the oven door is closed, the contacts (COM-

NO) must be closed.

2.  When the oven door is opened, the contacts (COM-

NO) must be opened.

f the oven door is opened and the contacts

(COM-NO) of the monitored latch switch SW1
fail to open, the fuse F1 blows simultaneously
with closing the contacts (COM-NC) of the
monitor switch SW2.

CAUTION:  BEFORE REPLACING A BLOWN

FUSE F1 TEST THE MONITORED
LATCH SWITCH SW1, MONITOR
SWITCH SW2.

Ensure the following:

1. Wires must not touch:

a) High voltage parts.
    (Magnetron, high voltage transformer, high voltage capacitor and high voltage rectifier assembly)
b) Parts that become hot.
    (Heating elements, oven lamp, oven cavity magnetron and high voltage transformer)
c) Sharp edges.
    (Bottom plates, oven cavity, waveguide flange, chassis support and other metallic parts)
d) Movable parts.
    (Fan blade, any motor, switch, switch lever and open button)

2. Positive lock connectors are fitted correctly.
3. Wires are connected correctly as per pictoral diagram.
4. No wire leads are trapped by the outer wrap.

Before carrying out any work; carry out 3D checks.
1.

isconnect the supply.

2.

oor opened, and wedged open.

3.

ischarge the high voltage capacitor.

LATCH
HEADS

LATCH HOOK

MONITOR
SWITCH (SW2)

MONITORED
LATCH
SWITCH (SW1)

STOP
SWITCH
(SW3)

DOOR OPEN BUTTON

OPEN LEVER

DOOR

R353M - 6

      

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. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit

with an A.C. voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.

6. RY1 and RY3 TEST
   These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during

the microwave cooking operation.

DC. voltage indicated .............. Defective relay.
DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good,

control unit is defective.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 18.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY3

APPROX. 18.0V D.C.

High voltage transformer

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

R353M - 7

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

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

2.  Control Unit

The following symptoms indicate a defective control unit. Replacing the control unit.

2-1  In connection with pads.

a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads 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.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.

2-3  Other possible problems caused by defective control unit.

a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
is making good contact, verify that the door sensing switch (stop switch) operates properly; that is the
contacts are closed when the door is closed and open when the door is open. If the door sensing
switch (stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control
unit and make sure the door sensing switch is closed (either close the door or short the door sensing
switch connecter). Use the Key unit matrix indicated on the STOP/CLEAR pad making momentary
contact. If the control unit responds by clearing with a beep the key unit is faulty and must be replaced.
If the control unit does not respond, it is a faulty and must be replaced. If a specific pad does not
respond, the above method may be used (after clearing the control unit) to determine if the control
unit or key pad is at fault.

1 min.

POWER

LEVEL

MINCED

MEAT

ROAST

PORK

ROAST

POULTRY

KITCHEN

TIMER

CHICKEN

PORTIONS

AUTO

COOK

LESS

Kg / Lb

MORE

SOUP

Express

DEFROST

STOP

CLEAR

10 sec.

10 min.

START

CLOCK

AUTO

MINUTE

AUTO

START

ROAST

BEEF/

LAMB

G12

G11

G10

G 9

G 1

G 2

G 3

G 4

G 5

G 6

G 7

G 8

DOWN

UP

R353M - 8

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for
burning damage and examine the
transformer with tester for the
presence of layer short-circuit (check
primary coil resistance). If any
abnormal condition is detected,
replace the defective parts.

CARRY OUT 4R CHECKS.

To protect the electronic circuits, this model is provided with a fine foil pattern added to the
primary on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the
troubleshooting guide given below for repair.

Problem: POWER ON, indicator does not light up.

CARRY OUT 3D CHECKS.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present at

Check supply voltage and oven power cord.

POWER terminal of CPU connector (CN-A).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

3

Only pattern at "a" is broken.

*Insert jumper wire J1 and solder.

(CARRY OUT 3D CHECKS BEFORE REPAIR)

4

Pattern at "a" and "b" are broken.

*Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

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. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit with

an A.C. voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.

6. RY1 and RY3 TEST
   These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the

microwave cooking operation.

DC. voltage indicated .............. Defective relay.
DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good,

control unit is defective.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 18.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY3

APPROX. 18.0V D.C.

High voltage transformer

CN - A

AC

31

VRS1

(J1)