Servicing For Touch Control Panel - Sharp R-990KS Service Manual

R990K(W)

[4] 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 outputter-
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 all 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. Shapes of Electronic Components
B
C
E
Transistor
2SB1238
3. 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 performthe 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, when checking the performance of the touch control
panel, put the outer cabinet on the oven to avoid touching the high
voltage transformer, or unplug the primary terminal (connector) of
the high voltage transformer to turn it off; the end of such connector
must be insulated with an insulating tape.After servicing, be sure to
replace the leads to their original locations.
1) 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 sepa-
rated.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.
2) On some models, the power supply cord between the touch control
panel and the oven proper is long enough that they may be sepa-
rated from each other. For those models, therefore, it is possible to
check and repair the controls of the touch control panel while keep-
ing 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
equivalent to the oven door being closed. As for the sensor-related
controls of the touch control panel, checking them is possible if
dummyresistor(s) with resistance equal to that of the controls are
used.
approx. 1M ohm
Transistor
DTA123ES
KRA101M
C B
KRA223M
E
KRC243M
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. Connect an exter-
nal power source to the power input terminal of the touch control
panel, then it is possible to check and repair the controls of the
touch control panel it is also possible to check the sensor-related
controls of the touch control panel by using the dummy resistor(s).
4. Servicing Tools
Tools required to service the touch control panel assembly.
1) Soldering iron: 60W
(It is recommended to use a soldering iron with a grounding termi-
nal.)
2) Oscilloscope: Single beam, frequency range: DC - 10MHz type or
more advanced model.
3) Others: Hand tools
5. Other Precautions
1) Before turning on the power source of the control unit, remove the
aluminium foil applied for preventing static electricity.
2) Connect the connector of the key unit to the control unit being sure
that the lead wires are not twisted.
3) After aluminium foil is removed, be careful that abnormal voltage
due to static electricity etc. is not applied to the input or output ter-
minals.
4) Attach connectors, electrolytic capacitors, etc. to PWB, making
sure that all connections are tight.
5) Be sure to use specified components where high precision is
required.
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