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R-952M  -  5

Damper position is set automatically by damper motor,
damper switch, damper cam and damper shaft.
These components are operated by a signal that
judges if microwave cooking or other cooking opera-
tion is selected by the CPU unit.

Damper is in the open position, because a portion of
cooling air is channeled through the cavity to remove
steam and vapors given off from the heating foods.
It is then exhausted at the top of the oven cavity into a
condensation compartment.

Damper is in the closed position, so that no hot air will
be allowed to leak out the oven cavity.

1. When power supply cord is plugged in:
1-1. When power supply cord is plugged in, a signal is

sensed in the control unit, and operates shut-off
relay (RY6).

1-2. Contacts of shut-off relay (RY6) close, the damper

motor is energized, opening the damper door.

1-3. When the damper is moved to the open position

by the damper cam, damper switch is closed (ON
position).

1-4. The signal of damper switch is re-sensed in the

control unit and shut-off relay (RY6) is turned off.

1-5. The A.C. line voltage A.C. to the damper motor is

stopped and the motor turns off.

2. When oven is microwave cooking:

Damper is in the open position

3. When oven is convection cooking:
3-1 Damper motor is energized right after the oven is

started.

3-2. When damper is in the closed position (damper

switch is OFF), its signal is sensed by the control
unit, and shut-off relay (RY7) is de-energized.

The door can be opened by pushing the open button on
the control panel.  When the open button is pushed, the
open lever pushes lower latch head on the door
upward.  The upper latch head is linked with the lower
latch head, so now, the door can be opened.

3-3. The damper is held in the closed position during the

cooking operation

3-4. At the end of any cooking, when the fan motor stops,

the relay (RY6) is energized and the damper is
returned to the open position.

NOTE: If the damper door is not in the proper position,

closed durining convection, grill or dual, or open
durning microwave, the control unit will stop oven
operation after 1 minute.

4. Operation of damper is shown below;

Damper operation

Cooking condition

Operation of Damper

Microwave

Convection

Grill; during backed up with con

vection heater

Grill; after convection heater

back- up has stopped.

Dual (Microwave and Convec

tion) when oven tempera
ture above 220˚C is pro
grammed.

When oven  temperature be-
low 200˚C is programmed.

Dual (Microwave and Grill)

Fire sensing condition

Open

Close

Close

Open

Close but open after 20 min-
utes.

Close

Open

Close

This model incorporates a sensing feature which will stop
the oven's operation if there is a fire in the oven cavity
during microwave cooking.
This accomplished by the LSI repeatedly measures the
voltage across the temperature measurement circuit (ther-
mistor) during it's 32-seconds time base comparing the
obtained voltage measurements. If the most recent  volt-
age measured is 300mV grater than the previous voltage
measured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the high voltage transformer, fan
motor and convection motor. The LSI also stops counting
down and closes the damper door so that no fresh air will
enter the oven cavity. Please refer to the following section
for a more detailed description.

Please refer to the timing diagram on page 4.

1. The thermistor operates within a 32-seconds time base

and it is energized for three (3) seconds and off for 29
seconds.  Two (2) seconds after the thermistor is
energized, the voltage across the temperature meas-
urement circuit is sampled by the LSI and twenty one
(21) seconds after the thermistor is cut off the LSI turns
on the cooling fan for six (6) seconds.

2. The above procedure is repeated. If the difference

between the first voltage measured (in step 1) and the
voltage measured when the procedure is repeated
(step 2) is greater than 300mV the LSI makes the
judgment that there is a fire in the oven cavity and will
switch off the relays to the high voltage transformer, fan
motor and convection motor. The LSI also stops count-
ing down and closes the damper door so that no fresh
air will enter the oven cavity.

Upper latch head

Lower latch 
head

Door

SW3 Monitor switch

SW1 Monitored
. latch switch

SW2 Stop switch

Open lever

R-952M  -  6

3. Once the fire sensor feature has shut the unit down,

the programmed cooking cycle may be resumed by
pressing the "START" pad or the unit may be reset by
pressing the "CLEAR" pad.

CONVECTION

MOTOR

THERMISTOR

Sensing 

Voltage

ON

OFF

ON

OFF

ON

OFF

0

21

27 29

64 (sec.)

Sensing the voltage across temperature measurement circuit.

6 sec.

3 sec.

The power output of this oven is rated using the method specified by IEC-705.  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).

Using this procedure, the heating time to raise 1000g of water by 10

°

C is approximately 50 seconds.

The IEC-705 procedure must be carried out using laboratory-type procedures and equipment.  These requirements
make the procedure unsuitable for routine performance checks.  An indication of the power being produced by the
oven
can however be obtained using the procedure given below.

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 70.

MICROWAVE LEAKAGE TEST

This oven should be tested for microwave leakage on completion of any repair or adjustment, following the proce-
dure 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 signifi-

cant 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

1. If the temperature of the thermistor does not rise  to

more than 40˚C after 4 minutes and 15 seconds
from when the oven is started in convection, grill or
dual cooking (Microwave and Convection) mode,
the oven is turned off.

2. When the thermistor or the wire harness to the

thermistor is opened, the oven is turned off after 4
minutes and 15 seconds because this condition is
same as above.

R-952M  -  7

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon
cable is marking 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 control panel
schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad
marking 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 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.

CARRY OUT 4R CHECKS.

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance can not 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 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 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 Panel

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

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 up.
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 troubles 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.
d) Proper temperature measurement is not obtained.

G 8

G 7

G 6

G 5

G 4

G 3

G 2

G 1

G12

G11

G10

G 9

MORE

info

Kg / Lb

SAUSAGE/

BURGER

CHIKEN

PORTIONS

FRESH

FISH

FRESH

VEG.

BAKED

POTATOES

ROAST

POTATOES

RICE/

PASTA

OVER

CHIPS

AUTO

COOK

GRILL

STOP/

CLEAR

MICROWAVE

POWER

LEVEL

CONVECTION

( ˚ C )

DUAL

CONVECTION/

GRILL

10 sec.

g • oz

Kg • Lb

TIMER

10 min.

1 min.

START

CLOCK

AUTO

MINUTE

AUTO

START

YORKSHIRE

PUDDING

AUTO

DEFROST

LESS

R-952M  -  8

(CARRY OUT 3D CHECKS BEFORE REPAIR.)

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

visual inspection of the varistor for burn-
ing damage and examine the trans-
former 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.

CARRY OUT 3D CHECKS.

Remove the outer case and check voltage between Pin Nos. 1 and 3 of the 4 pin connector (E) on
the control unit with an A.C. voltmeter.
The meter should indicate 230-240 volts, if not check oven circuit.

Relay Test
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill
operation, convection operation or dual 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

RY2

Approx. 18.0V D.C.

High voltage transformer

RY3

Approx. 24.0V D.C.

Grill heaters (Top)

RY4

Approx. 24.0V D.C.

Convection heater

RY5

Approx. 24.0V D.C.

Touch control transformer

RY6

Approx. 24.0V D.C.

Fan motor

RY7

Approx. 24.0V D.C.

Convection motor

RY8

Approx. 24.0V D.C.

Damper motor

CARRY OUT 4R CHECKS.

To protect the electronic circuits, this model is provided with a fine foil pattern added to the input
circuit 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 between

Check supply voltage and oven power cord.

Pin Nos. 1 and 3 of the 4-pin connector (E).

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".

7

9

1

RY4

(J2)

FM

POWER

F

CN - E

CN - A

VRS1

RY6