R21LCF
9 – 1
R21LCF
Service Manual
CHAPTER 9.
TOUCH CONTROL PANEL ASSEMBLY
[1] OUTLINE OF TOUCH CONTROL PANEL
1. Control Unit
Control unit consists of LSI, power source circuit, synchronizing signal
circuit, reset circuit, buzzer circuit, encoder circuit and indicator circuit.
1) LSI
This LSI controls the encoder signal, relay driving signal for oven
function, buzzer signal and LED signal.
2) Power Source Circuit
This circuit generates voltage necessary in the control unit.
Symbol Voltage Application
VC +5V (*) LSI(I-1)
VR +20V (*) RELAY(RY1, RY2)
(*) The voltage under the condition when all LEDs light up. The
voltage VR will vary according to the quantity of the LEDs which
light up
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) Reset 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 audible
sounds (completion sound).
6) Door Sensing Switch
A switch to “tell” the LSI if the door is open or closed.
7) Relay Circuit
To drive the magnetron, fan motor, antenna motor and light the
oven lamp.
8) Encoder
The encoder generates the pulse signal, and the pulse signal is
sent to the LSI.
9) Indicator Circuit
Indicator elements are the Light-emitting diodes (LD1- LD20).
This circuit consists of 4-digits and 5 segments.
[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.
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.
6) After that procedure, re-connect the power supply cord.
After checking the performance of the touch control panel,
1) Disconnect the power supply cord.
2) Open the door and block it open.
3) Re-connect the leads to the primary of the power transformer.
4) Re-install the outer case (cabinet).
5) Re-connect the power supply cord after the outer case is
installed.
6) Run the oven and check all functions.
a) On some models, the power supply cord between the touch
control panel and the oven itself is so short that the two can't
be separated. For those models, check and repair all the
controls (sensor-related ones included) of the touch control
panel while keeping it connected to the oven.
b) On some models, the power supply cord between the touch
control panel and the oven proper is so long enough that
they may be separated from each other. For those models,
therefore, it is possible to check and repair the controls of the
touch control panel while keeping it apart from the oven
proper; in this case you must short both ends of the door
sensing switch (on PWB) of the touch control panel with a
jumper, which brings about an operational state that is equiv-
alent to the oven door being closed. As for the sensor-
related controls of the touch control panel, checking them is
possible if the dummy resistor(s) with resistance equal to
that of the controls are used.
2. Servicing the touch control panel with power supply from an exter-
nal power source:
Disconnect the touch control panel completely from the oven
proper, and short both ends of the door sensing switch (on PWB) of
the touch control panel, which brings about an operational state
that is equivalent to the oven door being closed.
approx. 1M ohm
