Sharp R-4H56 Service Manual Download Page 25

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R-4H56

SERVICING

Transistor
2SB793

Transistor
DTA114YS
DTA143ES
DTB143ES
DTD143ES
2SA933S
2SC1740S

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 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.

approx. 1M ohm

2.. Shapes of Electronic Components

C B

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 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 DUR-
ING SERVICING AND PRESENTS A HAZ-
ARD.

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.

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 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) 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