Sharp R-3A88 Service Manual Download Page 19

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R-3A88

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 precautions should
be strictly followed. CMOS LSI have extremely high imped-
ance at its input and output terminals. For this reason, it is
easily influenced by the surrounding high voltage power
source, static electricity charge in clothes, etc. and some-
times 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.

approx. 1M ohm

2. Shapes of Electronic Components

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 supply 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 MICRO-
WAVE OVEN IS STILL LIVE DURING SERVICING
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; and the end of such connector must 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 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 is 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 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 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: 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

5. Other Precautions
1) Before turning on the power source of the control unit,

remove the aluminium foil applied for preventing static
electricity.

2) After aluminium foil is removed, be careful that abnormal

voltage due to static electricity etc. is not applied to the input
or output terminals.

3) Attach connectors, electrolytic capacitors, etc. to PWB,