Touch Control Panel Assembly - Sharp R-27STM Service Manual

R-27STM
The touch control section consists of the following units as shown in the touch control panel circuit.
(1) Switch Unit
(2) Control Unit
The principal functions of these units and their related signals are explained below.
Switch Unit
The switch unit is composed of a matrix, signals generated in the LSI are sent to the switch unit through P22, P24, P25 and P26.
When a button is pressed, a signal is completed through the switch unit and passed back to the LSI through P50 and P52 to perform
the function that was requested. When the jog dial is rotated, the encoder converts the signal from the power source circuit into the
pulse signal, and the pulse signal is sent to the LSI through P31 and P32.
Control Unit
Control unit consists of LSI, reset circuit, indicator circuit, power source circuit, relay circuit, buzzer circuit and synchronizing signal cir -
cuit.
1) Reset Circuit
This circuit generates a signal which resets the LSI to the initial state when power is supplied.
2) Indicator Circuit
This circuit consists of 4 -digits, 12 -segments and 3 -common electrodes using a Liquid Crystal Display.
3) Power Source Circuit
This circuit generates voltage necessary in the control unit from the AC line voltage. In addition, the synchronizing signal is
available in order to compose a basic standard time in the clock circuit.
Symbol Voltage
VSS -5V
4) Relay Circuit
To drive the magnetron, fan motor, turntable motor and light the oven lamp.
5) Buzzer Circuit
The buzzer is responsive to signals from the LSI to emit audible sounds (switch unit touch sound and completion sound).
6) 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.
7) 2nd. Interlock Relay Control Switch
A switch to "tell" the LSI if the door is open or closed.
8) Back Light Circuit
A circuit to drive the back light (Light emitting diodes LD1 - LD4).
1. Precautions for Handling Electronic Components
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 in -
fluenced 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.
R27STM.indd 12

TOUCH CONTROL PANEL ASSEMBLY

OUTLINE OF TOUCH CONTROL PANEL
Application
LSI(IC1)
SERVICING FOR TOUCH CONTROL PANEL
approx. 1M ohm
2. Servicing of Touch Control Panel
We describe the procedures to permit servicing of the touch
control panel of the microwave oven and the precautions 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.
1) Servicing the touch control panel with power supply of
the oven:
CAUTION: THE HIGH VOLTAGE TRANSFORMER OF THE MI -
CROWAVE OVEN IS STILL LIVE DURING SERVIC -
ING AND PRESENTS A HAZARD.
Therefore, 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.
Discharge high voltage capacitor.
(3) Disconnect the leads to the primary of the power
transformer.
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