R-770AM - Sharp Home Appliance Service Manual (repair manual). Page 10

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9
770AM -
TOUCH CONTROL PANEL ASSEMBLY
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 principal functions of these units and signals commu-
nicated among them are explained below.
Key Unit
The key unit is composed of a matrix, signals generated in
the LSI are sent to the key unit through P23 - P27.
When a key pad is touched, a signal is completed through
the key unit and passed back to the LSI through P74 - P77
to perform the function that was requested.
Control Unit
Control unit consists of LSI, power source circuit, synchro-
nizing signal circuit, ACL circuit, buzzer circuit, tempera-
ture measurement circuit, indicator circuit, encoder circuit
and back light circuit.
1) LSI
This LSI controls the temperature measurement sig-
nal, the 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.
Symbol
Voltage
Application
VC
-5.2V
LSI(IC1)
3) 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 commercial frequency.
4) ACL
A circuit to generate a signals 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, heating element, fan motor,
turntable motor and light the oven lamp.
8) Encoder
The encoder converts the signal generated by LSI into
the pulse signal, and the pulse signal is returned to the
LSI.
9) Back Light Circuit
A circuit to drive the back light (Light emitting diodes
LD1 - LD5).
10) Indicator Circuit
This circuit consists of 4-digits, 30-segments and 3-
common electrodes using a Liquid Crystal Display.
11) Temperature Measurement Circuit
The temperature in the oven cavity is sensed  by the
thermistor.
The variation of resistance according to sensed tem-
perature is detected by the temperature measurement
circuit and the result applied to LSI.
The result of detecting is given to LSI controlling the
relay and display.
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