Chapter 9. Touch Control Panel Assem; Outline Of Touch Control Pan; Servicing For Touch Control Panel - Sharp R-939(BK) Service Manual

R939(W)
CHAPTER 9.
R939(W)
TOUCH CONTROL PANEL ASSEMBLY
[1] OUTLINE OF TOUCH CONTROL PANEL
The control section consists of the following units as shown in the con-
trol panel circuit.
(1) Jog and Switch 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. Jog and Switch Unit
1) Tact switch circuit
The jog and switch unit is composed of a matrix, signals generated
in the LSI are sent to the jog and switch unit from P10, P11, P12,
P13, P14, P15, P16 and P17. When a tact switch pad is touched, a
signal is completed through the jog and switch unit and passed
back to the LSI through P70, P71, P72 and P73 to perform the
function that was requested.
2) Encoder
The encoder converts the signal generated by LSI into the pulse
signal, and the pulse signal is returned to the LSI.
3) Potentiometer circuit
The circuit makes setting of the cooking mode by variable resis-
tance.
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 and back light circuit.
1) LSI
This LSI controls the temperature measurement signal, tact switch
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

[2] SERVICING FOR TOUCH CONTROL PANEL

1. Precautions for Handling Electronic Components
This unit uses CMOS LSI in the integral part of the circuits. When han-
dling these parts, the following precautions should be strictly followed.
CMOS LSI have extremely high impedance at its input and output ter-
minals. For this reason, it is easily influenced 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.
Application
approx. 1M ohm
Service Manual
VC
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.
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 exter-
nal power source.
1. Servicing the touch control panel with power supply of the
oven:
CAUTION: THE HIGH VOLTAGE TRANSFORMER OF THE MICRO-
WAVE OVEN IS STILL LIVE DURING SERVICING 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.
3) Discharge high voltage capacitor.
4) Disconnect the leads to the primary of the power transformer.
5) Ensure that these leads remain isolated from other components
and oven chassis by using insulation tape.
9 – 1
-5.2V LSI(IC1)