R969(W)
9 – 1
R969(W)
Service Manual
CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
[1] OUTLINE OF TOUCH CONTROL PANEL
The touch control section consists of the following units as shown in
the touch control panel circuit.
(1) Key Unit
(2) Control Unit (The Control unit consists of Power unit and CPU unit.)
The principal functions of these units and signals communicated
among them are explained below.
1. Key Unit
The key unit is composed of a matrix, signals generated in the LSI are
sent to the key unit from P10, P11, P12, P13, P14, P15, P16 and P17.
When a key pad is touched, a signal is completed through the key unit
and passed back to the LSI through P70, P71, P72 and P73 to perform
the function that was requested.
2. Control Unit
Control unit consists of LSI, power source circuit, synchronizing signal
circuit, ACL circuit, buzzer circuit, relay circuit, temperature measure-
ment circuit, indicator circuit, absolute humidity sensor circuit and back
light circuit.
1) LSI
This LSI controls the temperature measurement signal, absolute
humidity sensor signal, key strobe signal, relay driving signal for
oven function and indicator signal.
2) Power Source Circuit
This circuit generates voltage necessary in the control unit.
3) Synchronizing Signal Circuit
The power source synchronizing signal is available in order to com-
pose a basic standard time in the clock circuit. It accompanies a
very small error because it works on commercial frequency.
4) ACL
A circuit to generate a signal which resets the LSI to the initial state
when power is supplied.
5) Buzzer Circuit
The buzzer is responsive to signals from the LSI to emit audible
sounds (key touch sound and completion sound).
6) Door Sensing Switch (Stop Switch)
A switch to “tell” the LSI if the door is open or closed.
7) Relay Circuit
To drive the magnetron, grill heating element, convection heating
element, convection motor, fan motor, turntable motor, damper
motor, touch control transformer and light the oven lamp.
8) Back Light Circuit
A circuit to drive the back light (Light emitting diodes LD10 - LD19).
9) Indicator Circuit
This circuit consists 40-segments and 16-common electrodes using
a Liquid Crystal Display.
The Liquid Crystal Display (LCD) is drive by LCD driver IC3.
10)Temperature Measurement Circuit: (OVEN THERMISTOR)
The temperature in the oven cavity is sensed by the thermistor. The
variation of resistance according to sensed temperature is detected
by the temperature measurement circuit and the result applied to
LSI. The LSI uses this information to control the relay and display
units.
11)Damper Switch
A switch to tell the LSI if the damper is open or close.
12)Absolute Humidity Sensor Circuit
This circuit detects the humidity of the food which is being cooked,
to control its automatic cooking.
[2] ABSOLUTE HUMIDITY SENSOR CIRCUIT
1. 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.
2. Operational Principle of Absolute Humidity Sen-
sor
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 ther-
mistors are placed in different humidity conditions they show different
degrees of heat conductivity leading to a potential difference 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 amplifier.
Symbol Voltage Application
VC -5.2V LSI(IC1)
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 )
O
u
t
p
u
t voltage
Absolute humidity vs,
output voltage characteristic
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