R-4G75M (serv.man3). Section 2 Test procedures, LSI table (page 8-22) - Sharp Home Appliance Service Manual (repair manual). Page 15

22

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 termi-
nals. For this reason, it is easily influenced by the sur-
rounding 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.

We describe the procedures to permit servicing of the
touch control panel of the microwave oven and the
cautions you must considre when doing so. To carry the
servicing, power supply to the touch control panel is
available either from the power line of the oven proper
itself of from an external power source.

from the oven proper:
CAUTION:
THE HIGH VOLTAGE TRANSFORMER OF THE MI-
CROWAVE OVEN IS STILL ALIVE TO GIVE YOU
DANGER DURING SERVICING.
Therefore, when checking the performance of the touch
control panel, put the outer cabinet on the oven proper to
keep from touching the high voltage transformer, or
unplug the primary terminal (connector) of the high
voltage transformer to turn it off; and the end of such
connector shall be insulated with an insulating tape. After
servicing, be sure to replace the leads to their original
locations.

A. On some models, the power supply cord between the

touch control panel and the oven proper is so short that
they can’t be separated from each other. For those
models, therefore,check and repair all the controls (with

approx. 1M ohm

Transistor
DTA114YS
DTA143ESXHZ
DTB143ES
DTD143ES
2SA933S

Transistor
2SB793

the sensor-related ones included) of the touch control
panel while keeping it in contact with the oven proper.

B. On some models, on the other hand, the power supply

cord between the touch control panel and the oven
proper is so long that they may be separated from each
other. For those models, therefore, it is allowed 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 stop switch (on PWB) of the
touch control panel with a jumper, which brings about an
operational state that is equivalent to the with the oven
door being closed. As to the sensor-related controls of
the touch control panel, their checking is allowed if the
dummy resistor(s) whose resistance is equal to that of
those controls are used.

from an external power source:
Disconnect the touch control panel completely from the
oven proper,and short both ends of the stop switch (on
PWB) of the touch control panel,which brings about an
operational state that is equivalent with the oven door
being closed. And connect an external power source to
the power input terminal of the touch control panel, and
then it is allowed to check and repair the controls of the
touch control panel; as in the case of (1)-B above, it is
here also possible to check the sensor-related controls of
the touch control panel by using the dummy resistor(s).

Tools required when servicing the touch control panel
assembly.

1) Soldering iron: 30W

 (To prevent leaking current, 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

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 connectors of the indicator and key unit to

the control unit taking care that the lead wires are not
twisted.

3) After aluminium foil is removed, take extra care 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,

taking care that all connections are tight.

5)  Be sure to use specified components where high preci-

sion is required.