Chapter 9. Touch Control Panel Assem; Outline Of Touch Control Panel; Servicing For Touch Control Panel - Sharp R-21LTF Service Manual

R21LTF
CHAPTER 9.
R21LTF
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 principal functions of these units and their related signals are
explained below.
1. Control Unit
Signal of key touch and oven function control are all processed by one
microcomputer.
1) Power Supply Circuit
This circuit changes output voltage at the secondary side of the low
voltage (T1) transformer to voltages required at each part by full
wave rectifying circuit, constant voltage circuit, etc..
2) ACL Circuit
This is an Auto-clear Circuit, i.e., a reset circuit, which enables IC1
to be activated from initial state.
3) Power SYNC Signal Generating Circuit
This is a circuit for generating power SYNC signal by virtue of the
secondary side output of transformer T1. This signal is used for a
basic frequency to time processing and so on.
4) Clock Circuit
This is a circuit for controlling clock frequency required for operat-
ing IC1.
5) IC1 (Main Processor)
This is a one-chip microcomputer, responsible for controlling the
entire control unit.
6) IC2 (Memory Processor)
This is a memory IC, responsible for memory function.
7) IC3
This is a IC for driving light emitting diode.
8) Display Circuit
This is a circuit for driving light emitting diode by IC1 output.
9) Key Input Circuit
This is a circuit for transmitting key input information to IC1.

[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.
approx. 1M ohm
Service Manual
10)Sound-body Driving Circuit
This is a circuit for driving sound body by IC1 output.
11)Relay Driving Circuit
This is a circuit for driving output relay by IC1 output.
12)Door Sensing Switch Circuit
This is a circuit for driving IC1 to detect door opening/ closing.
2. Key Unit
The key unit is composed of a matrix circuit in which when a key it
touched, one of signals P30--P34 generated by the LSI, is passed
through the key and returned to the LSI as one of signals P24--P27.
This model has 20 Memory pads. When the oven is shipped, Memory
pad 1 to 10 are set as follows: fig.1.
Memory No. Cook Time
1
2
3
4
5
6 1 min. 15 sec.
7 1 min. 30 sec.
8
9 2 min. 30 sec.
0
This model has a double quantity pad. When the oven is shipped,
Magnification "1.7" is preset in the double quantity pad. This model
has an express defrost pad. When the oven is shipped, express
defrost is set as follows: fig.2.
1 STAGE
FORMULA P = 0.2T
POWER 0.6
T : Total cooling time
When 1/2 total cooking time is passed, the signal will sound and
"CHECK" indicator will flash.
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.
9 – 1
Output Power
10 sec. 100%
20 sec. 100%
30 sec. 100%
45 sec. 100%
1 min. 100%
100%
100%
2 min. 100%
100%
3 min. 100%
(fig. 1)
2 STAGE
P = 0.15T
0.4
(fig. 2)
3 STAGE
P = 0.65T
0.2