Sharp R-9570 User manual

R-9570
.
SHARP SERVICE MANUAL
S7608R9570JII
MICROWAVE OVEN
MODEL R-9570
In the interests of user-safety the set should be restored to its original
condition and only parts identical to those specified be used.
This is a supplemental Service Manual for Model R-9570.
The R-9570 quite similar to Model R-9560.
Use this supplemental manual together with the Service Manual for Model R-9560.
Refer to the R-9560 Service Manual for complete operation, service information, etc.
TABLE OF CONTENTS
Page
FOREWORD ................................................................................................................................................. 1
CAUTION, MICROWAVE RADIATION .............................................................................................................. 1
THUMB INDEX ............................................................................................................................................... 1
PRODUCT DESCRIPTION .......................................................................................................................... 2-6
TOUCH CONTROL PANEL ASSEMBLY ...................................................................................................... 7-20
MICROWAVE MEASUREMENT ..................................................................................................................... 21
SCHEMATIC DIAGRAM ............................................................................................................................... 22
PICTORIAL DIAGRAM ............................................................................................................................ 23, 24
CONTROL PANEL CIRCUIT ..................................................................................................................... 25, 26
PRINTED WIRING BOARD ...................................................................................................................... 27, 28
PACKING AND ACCESSORIES ...................................................................................................................... 29
PARTS LIST ......................................................................................................................................... 30- 39
SHARP CORPORATION

R-9570
SERVICE MANUAL
SHARP
R-9570
FOREWORD
This Manual has been prepared to provide Sharp Service
Personnel with complete Operation and Service Information
for the Sharp Microwave Oven, R-9570.
The Model R-9570 is quite similar to the R-9560.
It is recommended that service personnel carefully study the
entire text of the two Manuals (R-9560 and R-95701, so they
will be qualified to render satisfactory customer service.
CAUTION
MICROWAVE RADIATION
Personnel should not be exposed to the microwave energy
which may radiate from the magnetron or other microwave
generating devices if it is improperly used or connected.
All input and output microwave connections, waveguides,
flanges, and gaskets must be secured.
Never operate the device without a microwave energy ab-
sorbing load attached.
Never look into an open waveguide or antenna while the
device is energized.
SHARP CORPORATION
OSAKA, JAPAN
PRODUCT DESCRIPTION 8PI
5 “I
?&[@’_-4TOUCH CONTROL
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- ‘*I- PARTS LIST

R-9570
PRODUCT DESCRIPTION
EXPLANATION OF MICROWAVE COOKING
The Sharp Counter Top Microwave Oven uses microwave ener- Materials with a high moisture content, like most foods, will
gy to produce heat in the food to be cooked. Unlike conven- absorb microwave energy. As the microwave energy at a fre-
tional ovens microwave energy will cook foods without quency of 2450 Megahertz enters the food, the molecules align
applying external heat. themselves with the energy. Because the microwave are
changing polarity every half cycle, the food molecules are
Microwaves, which are short electromagnetic waves of RF (ra-
dio frequency) energy, pass through materials such as glass,
paper, china and most plastics. Materials such as metal and
aluminum foil tend to reflect microwaves and may be used only
as recommended in the cooking instructions.
changing direction every half cycle or oscillating back and forth
4,900,000,000 times per second. This high speed oscillation
causes friction between the molecules, thereby converting the
microwave energy to heat.
SPECIFICATIONS
ITEMS
Power requirements
DESCRIPTIONS
240V
50Hz
Single phase, 3 wire earthed
Power consumption 1.4kW
Microwave output power
Case dimensions
Width
Height
Depth
Cooking cavity dimensions
Width
Height
Depth
Turntable diameter
700W (2 litre water load)
622mm
382mm
476mm
406mm
248mm
422mm
395mm
Control complement Ciock (l:OO- 12:59)
Minute Timer (O- 99 minutes 99 seconds)
Variable Cooking Mode Selector
Repetition Rate:
HIGH .........................
Full power throughout the cooking time
MED HIGH .................24 sec. ON, 8 sec. OFF, approx. 70% of full power
MED .......................... 18 sec. ON, 14 sec. OFF, approx. 50% of full power
MED LOW
DEFROST ...................12 sec. ON, 20 sec. OFF, approx. 30% of full pow&
LOW ..........................6 sec. ON, 26 sec. OFF, approx. 10% of full power
Auto Start Cooking
Instant Cooking
Compu. Defrost Cooking
Sensor Cook
Sensor Temp.
Temperature Control (30°C - 11OOC)
Neight Approx. 27kg
2

R-9570
1. Oven ‘door with see through window.
2. Oven lamp.
3. Removable turntable.
4. Removable temperature probe.
5. Temperature probe receptacle.
6. Door latches.
7. One touch door open button.
8. Auto-Touch control panel.
9. Lighted digital display.
10. Waveguide cover.
11. Ventilation openings.
Auto-TouchTM Control Panel
I- INDICATORS
COMPUMC0IOWMOHIGH
~~~~~13@I/r/ @ IT/
l&p QyIL//A-:!,//\//JJf
collx AU10 111
LIGHTED DIGITAL DISPLAY
Shows readout of cooking time, cooking instruction or time of day.
SENSOR COOK PAD
Touch to select Sensor Cook settings 1-O.
SENSOR COOK
I- FreshwgeL=Lws
2-Frozen“EqelaDles
3-Bakedpcmlces
rl - Frozen dmnen
5 -Bacon
NUMBER PADS
Touch to enter cooking times, clock time or weight of food.
a-he 8 pasti)
9-Meat I.xel
SENSOR TEMP PAD
Touch to select Sensor Temp settings l-7.
TEMP PAD
Touch to select temperature when using probe.
COMPU DEFROST PAD
Touch to select Compu Defrost settings 1 -5.
during cooking; touch twice
Touch to set Clock, Auto Start or Timer/Hold.
VARIABLE COOKING CONTROL PADS
Touch to select microwave power setting. If not touched, HIGH
is automatically selected.
START PAD
Touch to start oven.
INSTANT COOK PAD
Touch to cook for 1 minute at HIGH or increase by 1 minute
multiples during variable cooking.
3

COMPU DEFROST COOKING
Your Sharp Microwave Oven has special function keys to defrost meats and poultry faster and better.
Compu Defrost automatically defrosts roast beef, pork, steaks, chops, minced meat, whole chicken and
chicken pieces. Each key has 3 defrosting stages.
* Suppose you want to defrost a 1.O kg steak with CompuDefrost.
Step
1.
2.
3.
4.
5.
6.
Procedure
Touch the COMPU DEFROST pad.
Select desired Compu Defrost setting.
Touch 2 to defrost steak.
Touch number pads to enter weight.
Touch the START pad.
Open the door. Turn steak over and shield
any warm portions.
3eturn food to the oven.
lose the door.
Touch the START pad.
1 Pad Order
[COMP”DEFROST)
0
START
Display
j-1 will flash and COMPU
DEFROST will appear on display.
Kg. will flash on and off.
:u::;:,
Kg. stops flashing and remains on
display.
Defrosting time, variable power
of the first stage and COOK will
appear on display.
The timer will begin to count down. When the 1st stage
finishes, an audible signal will sound 4 times and oven
will stop. COOK indicator will go off.
rland -1 will be dis-
played repeatedly.
-1 and /STf,CTJ will be dis-
played repeatedly.
( ,,,,) -- fzfs-yq
The timer will begin to count down. When the 2nd stage
finishes, an audible signal will sound 4 times and oven
will stop. COOK indicator will go off.
[-and ImJ will be dis-
played repeatedly.

Step
7.
Procedure
Open the door. Turn steak over, remove
any thawed pieces and shield any warm
portions.
Return food to the oven.
Close the door.
8. Touch START pad.*
I Pad Order
i
I
Display
1-1 and lmT:-;‘R will be
displayed repeatedly.
The timer will begin to count
down. When the 3rd stage finish-
es, an audible signal will sound.
COOK indicator will go off.
[ST:=:] will be displayed con-
tinuously.
When door is opened or the STOP/CLEAR pad is touched, STAND will go out and the time of day will
appear on the display.
NOTE:
1. The weight can be entered in 0.1 kg increments. Kilograms must be rounded off to the nearest tenth
of a kilogram. (Example: 1.75 kg should be rounded off to 1.8 kg)
2. Foods weighting more or less than the quantity listed in the chart should be defrosted following guide-
lines in the cookbook. If the incorrect weight is entered and the START pad is touched -1 and
incorrect weight will be displayed repeatedly. The STOP/CLEAR pad has to be touched to reprogramme
the oven.

Compu DefrostTMChart
Compu Defrost Food
Setting Amount Display Procedure Comment
!----I
Minced 0.5 r- 1x-,-,rr7
L’ -li
,-I,L,lI l Before defrosting.. . Stand, covered
1 beef I 1-a(1_ - --1[ _“kJ’“Tl IO- 15 minutes.
2.5 kg -!’ ‘= .~-- _
.1
Steak 0.2 --r-i,,-, h7
I i- Jy‘&’,-ril
~~-/[yT=-\lrl l Before defrosting Stand, covered
2 /T/E- ”1:1
-= -- l Remove any thawed IO- 15 minutes.
2.0 kg pieces after each stage.
3
P
Whole
chicken
Roast beef
pork
lamb
1.0 r- ,-,-;T-=51
L.y)-f 1-lA.1
I mG;E3=Ep] l Before defrosting...
l After the 1st stage Stand, covered
3.0 kg ... If there are warm IO- 15 minutes.
portions, shield them. ...Stand a longer
lo r-;xm l After the 2nd stage time, if
JC=I“:EICl[Em-] ... Turn over and necessary.
shield the warm 15-20 minutes.
portions.
Chicken
pieces 0.2 /I l Before defrosting...
I j SL-
/=’c ;j:f’FFE- l After the 1st stage
1.5 kg ... Turn over and
rearrange. Stand, covered
[xl j--,“:mj l After the 2nd stage ... IO- 15 minutes.
Remove any thawed
pieces.
Pork chops 0.5
I pmTTJ l Before defrosting. .. Stand covered
Lamb chops iRE-1 [-yEmETf& l Remove any thawed IO- 15 minutes.
3.O’kg pieces after each stage.
L I I ,
6

TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOUCH CONTROL PANEL
The touch control section consists of the following units as
shown in the block diagram.
(1) Relay unit
(2) Key unit
(3) Control unit
Exchange of signals between each unit is indicated by the ar-
rows in the block diagram. The principal functions of these
units and the signals communicated among them are explained
below.
Relay Unit
Relay unit consists of two Relays (RY1 and RY2), power source
circuit and buzzer circuit.
Key Unit
The key unit is composed of a matrix, signals generated in the
LSI are sent to the key unit through E8, El 2, El 3, El 5, El 6
and E17.
When a key pad is touched, a signal is completed through the
key unit and passed back to the LSI through AN4-AN7 to per-
form the function that was requested.
Control Unit
Control unit consists of LSI (IX2429YA), power source circuit,
synchronizing signal circuit, ACL circuit, buzzer circuit, AH sen-
sor circuit, temperature measurement circuit and indicator
circuit.
1)
2)
3)
4)
5)
LSI (IX2429YA)
This LSI controls the AH sensor signal, temperature meas-
urement signal, key strobe signal, relay driving signal for
oven function, and indicator signal.
Power Source Circuit
This circuit generates voltage [VC (for IX2429YA): - 5V,
VF +: - 18.5V, VF-: -22V, VA: - 15V and Vp: -27Vl
necessary in the control unit.
Synchronizing Signal Circuit
The power source synchronizing signal is available in order
to compose a basic standard time in the clock circuit.
It accompanies a very small error because it works on com-
mercial frequency.
ACL Circuit
Circuit to generate signals resetting the LSI to the initial
state when power is supplied.
Buzzer Circuit
The buzzer is responsive to signals from the LSI to emit
noticing sounds (key touch sound and completion sound).
6)
7)
8)
9)
-- t
Absolute Humidity Sensor Circuit
Temperature Measurement Circuit
The temperature of food is measured by the probe. The
probe has a thermistor built in whose resistance varies
with the temperature. The variation of resistance is de-
tected by the temperature measurement circuit.
Stop Switch
A switch to “tell” the LSI if the door is open or closed.
Relay Circuit
To drive the magnetron, fan motor, turntable motor and
light the oven lamp.
10) Indicator Circuit
Indicator element is a Fluorescent Display.
Basically, a Fluorescent Display is a triode having a
cathode, a grid and an anode. Usually, the cathode of a
Fluorescent Display is directly heated and the filament
serves as cathode.
The Fluorescent Display 6-digits, 13-segments are used
for displaying figures.
This circuit detects absolute humidity of food which is
cooking, to allow automatic cooking.
7

I I G)
1 I n I m I 0 I 0 I w 1 D
FAN “0i-m
OYLN ‘AYP Am
TURN NLBLE
MOTOR
TO POWER
TRINSFORYLR
&gy” LATCH
[RELAY ClRC”lT]
n
Figure T-l. Block Diagram
I m I 0 I 0 I w I D

R-9570
DESCRIPTION OF LSI
LS I (K-l. IX2429YA)
The I/O signals of the LSI (IX2429YA) are detailed in the following tables.
EO
El
E2
E3
E4
E5
E6
E7
E8
E9
El0
El1
El2
El3
El4
El5
El6
El7
El8
El9
E20
E21
E22
E23
EX
X
RESET
SO/E24
SI/E25
E26
IRQ/E27
vss
25
26
27
28
29
30
31
32
LSI
ICI
IX2429YA
vcc
N.C
R15
R14
R13
R12
Rll
RlO
R9
R8
AN0
AN1
AN2
AN3
AN4
AN5
AN6
AN7
AVcc
AVa +
AVR-
AVss
E36
E37
R7
R6
R5
R4
R3
R2
Rl
RO
Figure T12. Relationship between pin Nos. and Signals (LSI: IX2429YA)
Pin No. Signal I/O Description
----”
1 EO OUT Digit selection signal. pl5oHzl
The relation between digit signal and digit are I2mru
2 El OUT as follows:
Digit Signal Digit
EO ii’____ ---!__--- ,’
3 E2 OUT EO ........................ 1st
El ........................ 2nd LJ-L- * 02mrec
4 E3 OUT E2 ........................ 3rd
E3 .I...................... 4th L.--rL
5 E4 OUT E4 ........................ 5th
E5 6th =n ........................
6 E5 OUT Normally, one pulse is output in every -n
\ fi period, and input to the grid of the GLlD
Fluorescent Display. ES -2N ~~
9

R-9570
Signal I/O Description
Pin No.
7 E6 OUT Segment data signals.
The relation between signals and indicators are as follows:
Signal Segment Signal Segment
E6 ........................ LB El 7 ......................... c, TEMP
E7 ....................... UB El 8 ......................... b, SENSOR
E9 .......................... i El 9 ........................ a, DEFROST
El0 ........................ j
El1 ...........a............ k
El2 ....................... h
El3 ....................... g
El4 ........................ f
El5 ........................ e PmoH2l
El6 ....................... d --J--l+n,-_r:;ix
I
~ZY’ n “tic””
I I
-1 '5 l.ZrnseC
! '
?zqy _ _ _ _ _ _ _ “%;““.
I I
-
1.A4 mrrc
8 E7 OUT 1) Segment data signal.
Signal similar to E6.
9 E8 OUT Key strobe signal.
Signal applied to touch-key section.
A pulse signal is input to AN4-AN7 terminal while one of G-2 line keys on key
matrix is touched.
10 E9 OUT Segment data signal.
Signal similar to E6.
El0
11
12
OUT
El1 OUT
Segment data signal.
Signal similar to E6.
1) Segment data signal.
Signal similar to E6.
13 El2 OUT 1) Segment data signal.
Signal similar to E6.
2) Key strobe signal.
Signal applied to touch-key section.
A pulse signal is input to AN4-AN7 terminal while one of G-3 line keys on
key matrix is touched.
10

RL9570
Pin No. Signal
14 El3
I/O
OUT I) Segment data signal.
Signal similar to E6.
Description
2) Key strobe signal.
Signal applied to touch-key section.
A pulse signal is input to AN4-AN7 terminal while one of G-4 line keys on
key matrix is touched.
15 El4 OUT Segment data signal.
Signal similar to E6.
16 El5 OUT 1) Segment data signal.
Signal similar to E6.
2) Key strobe signal.
Signal applied to touch-key section.
A pulse signal is input to AN4-AN7 terminal while one of G-5 line keys on
key matrix is touched.
17 El6 OUT 1) Segment data signal.
Signal similar to E6.
2) Key strobe signal.
Signal applied to touch-key section.
A pulse signal is input to AN4-AN7 terminal while one of G-6 line keys on
key matrix is touched.
18 El7 OUT 1) Segment data signal.
Signal similar to E6.
2) Key strobe signal.
Signal applied to touch-key section.
A pulse signal is input to AN4-AN7 terminal while one of G-7 line keys on key
matrix is touched.
19 El8
20 El9
21 E20
22 E21
23 E22
24 E23
25 EX
26 X
OUT
OUT
OUT
OUT
OUT
OUT
IN
OUT
Segment data signal.
Signal similar to E6.
Segment data signal.
Signal similar to E6.
Used for initial balancing of the bridge circuit (absolute humidity sensor).
Internal clock oscillation frequency setting input.
The internal clock frequency is set by inserting the ceramic filter oscillation circuit with
respect to X terminal.
Internal clock oscillation frequency control output.
Output to control oscillation input of EX.
11

R-9570
Pin Nc Signal
27 RESET
28 SO E24
29 SI E25
30 E26
31 IRQ E27
r
I/O Description
IN Auto-clear terminal.
Signal is input to reset the LS I to the initial state when power is supplied.
Temporarily set to “L” level the moment power is supplied, at this time the LS I is reset.
Thereafter set at “H” level.
OUT Terminal not used. Connected to GND.
Used for initial balancing of the bridge circuit (absolute humidity sensor)
OUT
OUT Signal to sound buzzer.
A: Key touch sound.
B: Completion sound.
A:
u
2.4 sec.
1
IN Signal synchronized with commercial power source
frequency.
This is the basic timing for all time processing
of LSI.
20 mrec.
32 vss IN Power source voltaae: -5V.
Vc voltage of power source circuit input.
33 RO OUT 1 I
HIGH
Magnetron high-voltage circuit driving signal.
To turn on and off the cook relay (RY2).
In HIGH operation, the signals holds “L” level
during microwave cooking and “H” level
while not cooking. In other cooking modes
(MED HIGH, MED, MED LOW, LOW) the sig-
nal turns to “H” level and “L” level in repeti-
tion according to the power level.
1
ON
24 let Bsac. ’
e L
ME0 HIGH OFF
ON
18 “C.
MED __ 14lac.
OFF
kLs---- L
- 1
ME0 LOW 12 sac. _ zosr.
DEFROST OFF
c
6uc. H GND
26 sec.
LOW -* F
OFF
-
‘ON -L
32 WC
I
I *,
HOLD H
34 Rl OUT Oven lamp and turntable motor driving signal (Square waveform: 50Hz).
To turn on and off shut-off relay (RY-1):
The Square waveform voltage (50Hz) is delivered to the RY 1 driving circuit and RY2.
Control circuit.
20 msec.
~-~-~----~-~--l~~--; GND
During cooking
12

RL9570
Pin No. Signal I/O Description
35-39 R2-R6 OUT Teminal not used. Connected to VC.
40 R7 IN Terminal not used. Connected to GND.
41 E37 IN Terminal to change the functions according to the Model.
Connected to El 9 Terminal by D 100 and R200.
42 E36
43 AVSS
44 AVR-
IN
IN
IN
Input signal which communicates the door open/close information to LSI.
Door closed; “H” level signal (OV).
Door opened; “L” level signal (-5V)
Connected to VC.
Reference voltage input terminal.
A reference voltage applied to the A/D converter in the LSI.
The reference voltage is generally maintained at -5V.
45 AVR +
46 AVCC
47 AN7
IN Reference voltage input terminal.
A reference voltage applied to the A/D converter in the LS I.
Connected to GND. (OV)
L
IN Connected to GND.
IN Signa! coming from touch-key.
When either one of G-l 1 line keys on key matrix is touched, a corresponding signal out
of E8, E12, E13, El 5, El 6 and El 7 will be input into AN7.
When no key is touched, the signal is held at “L” level.
48 AN6
49 AN5
IN
IN
Signal similar to AN7.
When either one of G-10 line keys on key matrix is touched, a corresponding signal will
be input into AN6.
Signal similar to AN7.
When either one of G-9 line keys on key matrix is touched, a corresponding signal will
be input into AN5.
50 AN4 IN Signal similar to AN7.
When either one of G-8 line keys on key matrix is touched, a corresponding signal will
be input into AN4.
51 AN3 IN Used for initial balancing of the bridge circuit (absolute humidity sensor).
This input is analog input terminal from the AH sensor circuit, and connected to the
A/D converter built into the LSI.
52 AN2 IN AH sensor input.
This input is an analog input terminal from the AH sensor circuit, and connected to the
A/D converter built into the LSI.
53 AN1
54 AN0
IN
IN
Terminal not used. Connected to GND.
Temperature measurement input.
By inputting DC voltage corresponding to the temperature detected by the temperature
probe, this input is converted into temperature by the A/D converter which is built in to
the LSI.
13

Pin No. Signal I/O Description \
55 R8 OUT Timing signal output terminal for temperature measurement and thermistor open
judgement.
~-f~~~~~~~
“H” level (GND): Temperature measuring timing.
“L” level (- 5V): Thermistor OPEN judging timing.
56-59 R9-R12 IN Terminal not used.
60 R13 IN Terminal for manufacture test.
Normally, terminal not used.
61 R14 IN Terminal not used. Connected to VC.
62 R15 IN Terminal for manufacture test.
Normally, connected to VC (--5V) by pull-down resistor,(R75).
63 NC NC Terminal not used. Connected to GND.
64 vcc IN Connected to GND.
14

R-9570
POWER SOURCE CIRCUIT
240 V AC power is applied to the primary winding of trans-
former (Tl). The output voltage of the secondary winding of
transformer (Tl ) is then full-wave rectified by the diode bridge
and smoothed by the electrolytic capacitor to become DC vol-
tage Vp.
Then the voltage Vp is delivered to the constant voltage circuit.
Symbol Voltage
VC -5v
Application
LSI (ICl), ACL circuit and
Temperature measurement
circuit.
VA -15v IC2.
VP
VI=+
VF-
-27V Fluorescent display tube.
: Grid and anode voltage.
- 18.5V Filament of fluorescent display
-22v tube: VF+ - VF- voltage.
Figure T-3.
SYNCHRONIZING SIGNAL CIRCUIT
The secondary winding output voltage of the transformer (Tl)
is half wave rectified, subjected to a voltage division by R21
and R23 and treated as a power source synchronizing signal.
T/C TRANSFORMER
LSI
ICl
c
31 IRO E27
This is the basic timing for all time processing.
C20: Noise filter capacitor.
D20: Clamp diode.
20msec.
Figure T-4.
15

ACL CIRCUIT
By switching on power, charge current (il) is fed to C30
through R30 and generates Vz voltage.
If Vz exceeds the threshold voltage of ZD30, ZD30 is turned
on and the current i2flows. Thus, placing voltage on to the base
of transistor 030 and turning it on.
A reset signal is obtained from the collector.
C31: Noise filter capacitor.
D30
VC 4 A I
RESET
This circuit is an oscillation circuit which is composed of piezo-
electric buzzer SP40 with feedback electrode and transistor 040.
041 works to switch on the buzzer circit and controls how
long the alarm continues to sound.
Figure T-5.
BUZZER CIRCUIT
LSI (IC 1) produces three types of alarm sound by emitting the
signal to control 041 as illustrated.
Figure T-6.
16

RL957o
TEMPERATURE MEASUREMENT CIRCUIT
Fig. T-7 shows the temperature measurement circuit. The ther-
mistor in the temperature probe varies in resistance accord-
ing to the cooking temperature and this variation is converted
to an analog voltage variation to be delivered to the AN0 ter-
minal of LSI which contains an A/D converter. In the LSI there
are produced “H” level and “L” level signals at its output ter-
minal R8, as shown in Fig. T-8.
When the output signal of the terminal R8 is at “H” level, tran-
sistor Q60 turns on to short R63, and the circuit equivalent
to that shown in Fig. T-9(a) is set up. With this equivalent cir-
cuit in operation, the LSI can perform the temperature meas-
urement through the temperature probe.
TE MP
PROBE
When the output signal of terminal R8 is at “L” level, the tran-
sistor 060 turns off to get R61 and R63 connected in series
with each other, and the circuit equivalent to that shown in
Fig. T-9(b) is set up. With this equivalent circuit in operation,
the LSI judges whether the temperature probe is opened or
not: that is, when the temperature probe is opened, the vol-
tage almost equal to VREF/2 is applied to the AN0 terminal of
LSI; when it is not opened (at its normal state), the voltage
lower than VREF/2 is applied thereto. With the temperature
probe opened, the temperature indicator and numeral indica-
tor flash to indicate this state.
Figure T-7. Temperature Measurement Circuit
‘::‘#----J ~1 ------j-----.1::
:I
I 18 msec. 1
I 1-1
Figure T-8. Signal Output Timing at Q2 Terminal
PR. PR
R62
R62 -[To LSI( ICl 11
I-WCTo LSI ( ICl 13 R61
R61 R63
VC s VC z-
(a) R8 tcrminal”H” (bl I?8 terminal “C’
Figure T-9. Circuit Equivalent to Temperature Measurement Circuit
17

R-9570
ABSOLUTE HUMIDITY SENSOR CIRCUIT
(I) Structure of Absolute Humidity Sensor
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.
Sensinq Part Internal Structure of Sensor
OP
“CI
Vent hole
Figure T-10.
(2) Operational Principle of Absolute Humidity Sensor
The figure below shows the basic strcture of an absolute hu-
midity sensor. A bridge circuit is formed by two thermistors
and two resistors (Rl and R2).
The output of the bridge circuit is to be amplified by the oper-
ational amplifier.
Each thermistor is supplied with a current to keep itself heat-
ed at about 150°C (302OF) and the resultant heat is dissipat-
ed in the air and if the two thermistors are placed in different
humidity conditions they show different degrees of heat con-
ductivity leading to potential difference between them caus-
ing 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 will be amplified by the oper-
ational amplifier.
C: Thermistor in
closed vessel
Figure T.
Absolute humtdlty vs.
output voltage character IstIc
b
11. Absolute humldlty (g/m’ 1
(3) Detector Circuit of Absolute Humidity Sensor
This detector circuit is used to detect the output voltage of
the absolute humidity circuit to allow the LSI to control the
sensor cooking of the unit.
When the unit is set in the Sensor Cooking mode, 16 seconds
later the detector circuit starts to function and the LSI observes
the initial voltage available at its AN2 terminal. With this vol-
tage 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 R50-1. Changing the resistance values results in that there
is the same potential at both C-3 terminal of the absolute hu-
midity sensor and AN3 terminal of the LSI. The voltage of AN2
terminal will indicate about - 2.5V. This initial balancing is set
up about 16 seconds after the unit is put in the Sensor Cook-
ing mode.
As the sensor cooking proceeds, the food is heated to gener-
ate moisture by which the resistance balance of the bridge cir-
cuit is deviated to increase the voltage available at AN2
terminal of the LSI. Then the LSI observes that voltage at AN2
terminal and compares it with its initial value, and when the
comparison rate reaches the preset value (fixed for each menu
to be cooked), the LSI causes the unit to stop the sensor cook-
ing; thereafter, the unit gets in the next necessary opeation
automatically.
When the LSI starts to detect the initial voltage at AN2 termi-
nal 16 seconds after the unit has been put in the Sensor Cook-
ing mode, if it is impossible to take a balance of the bridge
circuit due to disconection of the absolute humidity sensor,
ERROR will reappear on the display and the cooking is stopped.
1) Absolute humidity sensor circuit
050
2)
0 RSO-517 23 E22d
it sw4-i
0
C Therm,.for ,n I I, MO-719 21
closed vessel I
s Thermastor tn
open *es,c,
LSI
( IC 1)
AN2
RS3
Figure T- 12.
internal equivalent circuit of 12
CH1 CH2
_-_--------- ---- -
Top View
VOLrTl
VIN(-)I
VIN(+)l
VF.E
Figure T-l 3.
VW
volrr2
VIN(-12
VIN(+)2
--f+4IN(-)2
.--+VIN(+)2
18