Sharp R-4H55 Service Manual page 28

SERVICING
1 .Precautions for Handling Electronic Components
This unit uses CMOS LSI in the integral part of the
circuits. When handling these parts, the following pre-
cautions should be strictly followed.
CMOS LSI have extremely high impedance at its input
and output terminals. For this reason, it is easily influ-
enced 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 aluminum foil. Also wrap all PW boards con-
taining 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
@
Transistor
Transistor
DTAll4YS
2SB793
DTAI 43ES
CB
DTBl43ES
DTDl43ES
E
2SA933S
2SC174OS
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 perform
the servicing, power to the touch control panel is avail-
able either from the power line of the oven itself or from
an external power source.
(1)Servicing the touch control panel with power sup-
ply of the oven:
CAUTION:
THE HIGH VOLTAGE TRANSFORMER OF THE
MICROWAVE OVEN IS STILL LIVE DURING SERV-
ICING 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 un-
plug the primary terminal (connector) of the high volt-
age transformer to turn it off; the end of such connector
must be insulated with an insulating tape. After servic-
ing, be sure to replace the leads to their original loca-
tions.
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 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 dummy resistor(s)
with resistance equal to that of the controls are used.
(2)Servicing the touch control panel with power sup-
ply 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 being 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 sen-
sor-related controls of the touch control panel by using
the dummy resistor(s).
4Servicing Tools
Tools required to service the touch control panel assem-
bly.
1) Soldering iron: 30W
(It is recommended to use a soldering iron with a
grounding terminal.)
2) Oscilloscope: Single beam, frequency range: DC-
1OMHz type or more advanced model.
3) Others: Hand tools
5.0ther Precautions
1) Before turning on the power source of the control unit,
remove the aluminum 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 aluminum foil is removed, be careful that abnor-
mal 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 specified components where high pre-
cision is required.
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