Sharp R-7H55, Service Manual

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20
R-7H55
TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOIUCH 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 the signals com-
municated 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 R20-R23. When a
key pad is touched, a signal is completed through the key
unit and passed back to the LSI through R80-R83, D10 and
D12-D13 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, indicator
circuit, relay circuit, temperature measurement circuit and
AH sensor circuit.
1) LSI
This LSI controls the key strobe signal, relay driving
signal for oven function and indicator signal.
2) Power Source Circuit
This circuit generates voltages necessary in the control
unit.
Symbol Voltage Application
VC -5.1V LSI(IC1)
VP -26V Fluorescent display tube : Grid
and anode voltage
VF1 2.9Vac Filament of fluorescent display
tube
VF2 (VF1 to VF2 voltage)
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 Circuit
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
noticing 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, fan motor, turntable motor and
light the oven lamp.
8) Indicator Circuit
Indicator element is a Fluorescent Display.
Basically, a Fluorescent Display is 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 has 6-digits, 14-segments are
used for displaying figures.
9) Temperature Measurement Circuit
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 result of detecting is given to LSI controlling the relay
and display.
10) Damper switch
A switch to tell the LSI if the damper is open or close.
11) AH Sensor Circuit
This circuit detects the moisture of a food which is
cooking, to allow its automatic cooking.