Servicing For Touch Control Panel - Sharp R-231NW Service Manual

[3] SERVICING FOR TOUCH CONTROL PANEL

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? uenced 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
? gure 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 external power source.
1 Servicing the touch control panel with power supply of the oven:
CAUTION: THE HIGH VOLTAGE TRANSFORMER OF THE
MICROWAVE OVEN IS STILL LIVE DURING
SERVICING AND PRESENTS A HAZARD.
Therefore, when 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.
approx. 1M ohm
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 equivalent 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
external 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 be-
ing closed. Connect an external 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).
3. Servicing Tools
Tools required to service the touch control panel assembly.
1) Soldering iron: 30W
(It is recommended to use a soldering iron with a grounding
terminal.)
2) Oscilloscope: Single beam, frequency range: DC - 10MHz
type or more advanced model.
3) Others: Hand tools
4. 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 be-
ing 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 terminals.
4) Attach connectors, electrolytic capacitors, etc. to PWB,
making sure that all connections are tight.
5) Be sure to use speci? ed components where high precision
is required.
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R-231NW