DOWNLOAD Sharp R-96 (serv.man3) Service Manual ↓ Size: 880.02 KB | Pages: 52 in PDF or view online for FREE

R-953/963M - 23

The absolute humidity sensor includes two thermistors
as shown in the illustration. One thermistor is housed
in the closed vessel filled with dry air while another in
the open vessel. Each sensor is provided with the
protective cover made of metal mesh to be protected
from the external airflow.

The figure below shows the basic structure of an
absolute humidity sensor. A bridge circuit is formed by
two thermistors and two resistors (R1 and R2).
The output of the bridge circuit is to be amplified by the
operational amplifier.
Each thermistor is supplied with a current to keep it
heated at about 150˚C, the resultant heat is dissipated
in the air and if the two thermistors are placed in
different humidity conditions they show different de-
grees of heat conductivity leading to a potential differ-
ence between them causing an output voltage from the
bridge circuit, the intensity of which is increased as the
absolute humidity of the air increases. Since the output
is very minute, it is amplified by the operational ampli-
fier.

cuit
This detector circuit is used to detect the output voltage
of the absolute humidity circuit to allow the LSI to
control sensor cooking of the unit.  When the unit is set
in the sensor cooking mode, 16 seconds clearing cycle
occurs than the detector circuit starts to function and
the LSI observes the initial voltage available at its AN1
terminal.

With this voltage given, the switches SW1 to SW5 in
the LSI are turned on in such a way as to change the
resistance values in parallel with R97 ~ R102.  Chang-
ing the resistance values results in that there is the
same potential at both F-3 terminal of the absolute
humidity sensor and AN0 terminal of the LSI. The
voltage of AN1 terminal will indicate about -2.5V. This
initial balancing is set up about 16 seconds after the
unit is put in the Sensor Cooking mode. As the sensor
cooking proceeds, the food is heated to generate
moisture by which the resistance balance of the bridge
circuit is deviated to increase the voltage available at
AN1 terminal of the LSI.
Then the LSI observes that voltage at AN1 terminal and
compares it with its initial value, and when the compari-
son rate reaches the preset value (fixed for each menu
to be cooked), the LSI causes the unit to stop sensor
cooking; thereafter, the unit goes in the next operation
automatically.
When the LSI starts to detect the initial voltage at AN1
terminal 16 seconds after the unit has been put in the
Sensor Cooking mode, if it is not possible to balance
the bridge circuit to disconnection of the absolute
humidity sensor, ERROR will appear on the display
and the cooking is stopped.

1) Absolute humidity sensor circuit

Sensing part
(Open vessel)

Sensing part
(Closed vessel)

C

S

R3

R1

R2

+

Operational
amplifier

Output
voltage

S : Thermistor
     open vessel

C : Thermistor
      closed vessel

2

Absolute humidity (g/m  )

Output voltage

Absolute humidity vs,
output voltage characteristic

SW1

SW2

SW3

SW4

SW5

P54

P53

P52

P51

P50

 LSI
(IC1)

AN0

AN1

620k

300k

150k

75k

37.4k

13

16

17

1

5

8

7

4

6

80

15

14

47k

47k

IC2

10k

0.01uF

0.015uF

0.01uF

+

VA : -15V

VA : -15V

R90

C90

C91

C93

C92

S

F-2

1.8k

F-1

F-3

C

3.57k

3.32k

VC : -5V

0.1 uF

C. Thermistor in 
    closed vessel
S. Thermistor in
    open vessel

R98

R99

R96

R91

360k

R93

R92

R94

R95

R100

R101

R102

R97

R-953/963M - 24

This unit uses CMOS LSI in the integral part of the circuits.
When handling these parts, the following precautions
should be strictly followed. CMOS LSI have extremely
high impedance at its input and output terminals. For this
reason, it is easily influenced by the surrounding high
voltage power source, static electricity charge in clothes,
etc., and sometimes it is not fully protected by the built-in
protection circuit.
In order to protect CMOS LSI.
1) When storing and transporting, thoroughly wrap them

in aluminium foil. Also wrap PW boards containing
them in aluminium foil.

2) When soldering, ground the technician as shown in

the figure and use grounded soldering iron and work
table.

We describe the procedures to permit servicing of the
touch control panel of the microwave oven and the pre-
cautions you must take when doing so.
To perform the servicing, power to the touch control panel
is available either from the power line of the oven itself or
from an external power source.

T

herefore, before checking the performance of the touch

control panel,
1) Disconnect the power supply cord, and then remove

outer case.

2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Disconnect the leads to the primary of the power

transformer.

5) Ensure that these leads remain isolated from other

components and oven chassis by using insulation
tape.

6) After that procedure, re-connect the power supply

cord.

After checking the performance of the touch control

panel,

1) Disconnect the power supply cord.
2) Open the door and block it open.
3) Re-connect the leads to the primary of the power

transformer.

4) Re-install the outer case (cabinet).

approx. 1M ohm

5) Re-connect the power supply cord after the outer

case is installed.

6) Run the oven and check all functions.

 On some models, the power supply cord between the

touch control panel and the oven itself is so short that
the two can't be separated.

For those models, check and repair all the controls
(sensor-related ones included) of the touch control
panel while keeping it  connected to the oven.

 On some models, the power supply cord between the

touch control panel and the oven proper is long enough
that they may be separated from each other. For those
models, therefore, it is possible to check and repair the
controls of the touch control panel while keeping it
apart from the oven proper; in this case you must short
both ends of the door sensing switch (on PWB) of the
touch control panel with a jumper, which brings about
an operational state that is equivalent to the oven door
being closed. As for the sensor-related controls of the
touch control panel, checking them is possible if the
dummy resistor(s) with resistance equal to that of the
controls are used.

Disconnect the touch control panel completely from
the oven proper, and short both ends of the door
sensing switch (on PWB) of the touch control panel,
which brings about an operational state that is equiva-
lent to the oven door being closed. Connect an exter-
nal power source to the power input terminal of the
touch control panel, then it is possible to check and
repair the controls of the touch control panel; it is also
possible to check the sensor-related controls of the
touch control panel by using the dummy resistor(s).

Tools required to service the touch control panel assem-
bly.
1) Soldering iron: 30W

(It is recommended to use a soldering iron with a
grounding terminal.)

2) Oscilloscope: Single beam, frequency range: DC -

10MHz type or more advanced model.

3) Others: Hand tools

1) Before turning on the power source of the control unit,

remove the aluminium foil applied for preventing static
electricity.

2) Connect the connector of the key unit to the control

unit being sure that the lead wires are not twisted.

3) After aluminium foil is removed, be careful that abnor-

mal voltage due to static electricity etc. is not applied
to the input or output terminals.

4) Attach connectors, electrolytic capacitors, etc. to PWB,

making sure that all connections are tight.

5) Be sure to use specified components where high

precision is required.

Transistor
2SB1238

Transistor
KRC243M

R-953/963M - 25

7. Lift the entire case from the oven.
8. Discharge the H.V. capacitor before carrying out any

further work.

10.Do not operate the oven with the outer case removed.
N.B.; Step 1, 2 and 8 form the basis of the 3D checks.

CAUTION: DISCHARGE HIGH VOLTAGE CAPACI-

TOR BEFORE TOUCHING ANY OVEN
COMPONENT OR WIRING.

1. Disconnect oven from power supply.
2. Visually check the door and cavity face plate for dam-

age (dents, cracks, signs of arcing etc.).

Carry out any remedial work that is necessary before
operating the oven.
Do not operate the oven if any of the following conditions
exist;
1. Door does not close firmly.
2. Door hinge, support or latch hook is damaged.
3. The door gasket or seal or damaged.

4. The door is bent or warped.
5. There are defective parts in the door interlock system.
6. There are defective  parts in the microwave generating

and transmission assembly.

7. There is visible damage to the oven.

Do not operate the oven:
1. Without the RF gasket (Magnetron).
2. If the wave guide or oven cavity are not intact.
3. If the door is not closed.
4. If the outer case (cabinet) is not fitted.

Please refer to ‘OVEN PARTS, CABINET PARTS, CONTROL PANEL PARTS, DOOR PARTS’, when carrying out any
of the following removal procedures:

To prevent an electric shock, take the following
manners.
1. Before wiring,

1) Disconnect the power supply.
2) Open the door and wedge the door open.
3) Discharge the high voltage capacitor and wait for

60 seconds.

2. Don't let the wire leads touch to the following parts;

1) High voltage parts:

Magnetron, High voltage transformer, High volt-
age capacitor and High voltage rectifier assem-
bly.

2) Hot parts:

Grill heating element, Convection heating ele-

ment, Oven lamp, Magnetron, High voltage trans-
former and Oven cavity.

3) Sharp edge:

Bottom plate, Oven cavity, Weveguide flange,
Chassis support and other metallic plate.

4) Movable parts (to prevent a fault)

Fan blade, Fan motor, Switch, Turntable motor,
Convection motor, Convection fan, Cooling fan.

3. Do not catch the wire leads in the outer case cabinet.
4. Insert the positive lock connector certainly until its pin

is locked. And make sure that the wire leads should
not  come off even if the wire leads is pulled.

5. To prevent an error function, connect the wire leads

correctly, referring to the Pictorial Diagram.

4. Remove one (1) screw holding earth side terminal of

the high voltage rectifier assembly to the base plate
through the capacitor holder.

5. Release the capacitor holder from the base plate.
8. Remove the high voltage capacitor from the capacitor

holder.

To remove the outer case proceed as follows.
1. Disconnect oven from power supply.
2. Open the oven door and wedge it open.
3. Remove the one (1) screw holding the air to the oven

cavity rear plate.

4. Remove the air duct.
5. Remove the nine (9) screws from rear and along the

side edge of case.

6. Slide the entire case back about 3 cm to free it from

retaining clips on the cavity face plate.

To remove the components, proceed as follows.
1. CARRY OUT 3D CHECKS.
2. Disconnect the filament lead of the high voltage trans-

former and the high voltage wire of the high voltage
transformer from the high voltage capacitor.

3. Disconnect the high voltage wire B from the high

voltage capacitor.

R-953/963M - 26

1. CARRY OUT 3D CHECKS.
2. Disconnect the main wire harness from the high volt-

age transformer.

3. Disconnect the filament leads and high voltage wire  of

high voltage transformer from high voltage capacitor

and the magnetron.

4. Remove the two (2) screws and one (1) washer holding

the transformer to the base plate.

5. Remove the transformer.
6. Now the high voltage transformer is free.

1. CARRY OUT 3D CHECKS.
2. Disconnect the H.V. wire B and filament lead of the

transformer from the magnetron.

3. Carefully remove four (4) screws holding the magnetron

to the waveguide, when removing the screws hold the
magnetron to prevent it from falling.

4. Remove the magnetron from the waveguide with care

so the magnetron antenna is not hit by any metal object
around the antenna.

5. Remove the magnetron guide H from the magnetron.
6. Remove the one (1) screw holding the magnetron

guide V to the magnetron.

7. Now, the magnetron is free.

CAUTION: WHEN REPLACING THE MAGNETRON,

BE SURE THE R.F. GASKET IS IN PLACE
AND THE MAGNETRON MOUNTING
SCREWS ARE TIGHTENED SECURELY.

NOTE:
1. Before attaching a new key unit, wipe off remaining

adhesive on the control panel frame surfaces com-
pletely with a soft cloth soaked in alcohol.

2. When attaching the key unit to the control panel frame,

adjust the upper edge and right edge of the key unit to
the correct position of  control panel frame.

3. Stick the key unit firmly to the control panel frame by

rubbing with soft cloth not to scratch.

1. CARRY OUT 3D CHECKS.
2. Disconnect the wire leads and the connectors from the

control unit.

3. Remove the one (1) screw holding the earth wire to the

oven cavity face plate.

4. Lift up the control panel assembly and pull it forward.

Now the control panel assembly is free.

2) Remove the fan blade assembly from the shaft of

the fan motor by pulling and rotating the fan blade
with your hand.

3) Now, the fan blade is free.

11.Remove the two (2) screws holding the fan motor to the

fan duct.

12.Now, the fan motor is free.

1. Install the the fan motor to the fan duct with the two (2)

screws and nuts.

2. Install the fan blade to the fan motor shaft according to

the following procedure.
1) Hold the centre of the bracket which supports the

shaft of the fan motor on a flat table.

2) Apply the screw lock tight into the hole  (for shaft) of

the fan blade.

3) Install the fan blade to the shaft of fan motor by

pushing the fan blade with a small, light weight,
rubber mallet.

1. CARRY OUT 3D CHECKS.
2. Remove the one (1) screw holding the noise filter to the

chassis support.

3. Release the noise filter from the tabs of the fan duct.
4. Remove the four (4) screws holding the chassis sup-

port to the oven cavity front flange, back plate, air
intake duct and the magnetron.

5. Remove the chassis support from the oven cavity.
6. Disconnect the wire leads from the fan motor.
7. Remove the one (1) screw holding the fan duct to the

back plate.

8. Release the tabs of the fan duct from back plate.
9. Remove the fan duct from the oven.
10.Remove the fan blade from the fan motor shaft accord-

ing to the following procedure.
1) Hold the edge of the rotor of the fan motor by using

a pair of groove joint pliers.

7. Disconnect the high voltage rectifier assembly from the

high voltage capacitor.

8. Now, the high voltage rectifier assembly and the high

voltage capacitor should be free.

CAUTION: WHEN REPLACING HIGH VOLTAGE

RECTIFIER ASSEMBLY, ENSURE THAT
THE CATHODE (EARTH) CONNECTION
IS SECURELY FIXED TO THE BASE
PLATE THROUGH THE CAPACITOR
HOLDER WITH AN EARTHING SCREW.