Sharp R-8470, Service Manual

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A -8470
-8570
SERVICING
Precautions for Handing Electronic
Components
This unit uses PMOS LSI in the integral part of the
circuits. When handing these parts, the following
precautions should be strictly followed.
PMOS 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 charged in clothes,
etc,and sometimes it is not fully protected by the
built-in protection circuit.
In order to protect PMOS LSI.
1) When storing and transporting, throughly wrap
them in aluminum foil.
Also wrap PW boards containing them in
aluminium foil.
2) When soldering,
ground the technician as
s h o w n i n t h e f i g u r e a n d u s e g r o u n d e d
soldering iron and work table.
Panel
We describe the procedures to permit servicing the
touch control panel of the microwave oven and the
cautions you must consider 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.
Therefore, when checking the performance of
the touch control panel,put the outer cabinet
on the oven proper to keep you from touching
the high voltage transformer, or unplug the
primary terminal (connector) of the high volt-
age transformer to turn it off; and the end of
such connector shall be insulated with an in-
sulating tape. After servicing, be sure to replace
the leads to their original locations.
A. On some models, the power supply cord be-
tween 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 the sensor-related ones
included) of the touch control panel while
keeping it in contact with the oven proper.
3.
4.
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 mod-
els, 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 opera-
tional state that is equivalent to that 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 is used.
Disconnect the touch control panel completely
from the oven proper,and short both ends of
the stop switch (on PWB) of the touch control
brings about such an operational
state that is equivalent that 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
in the case of (1 )-B above, it is here
also possible to check the sensor-related con-
trols of the touch control panel by using the
dummy resistor(s).
Tools required when the touch control
panel assembly.
1) Soldering:
3 o w
(To prevent leaking current, it is recommended to
use a soldering iron with grounding terminal.)
2) Oscilloscope: Single beam, frequency range:
DC type or more ad-
vanced model.
3) Others: Other tools
1) When turning on the power source of the con-
trol unit, remove the aluminum foil applied for
preventing static electricity.
2) Connect the connectors of the indicator and
key units to the control unit taking care that the
lead wires are not twisted.
3)
After aluminum foil is removed, take extra care
that abnormal voltage due to static electricity
etc. is not applied to the input or output termi-
nals.
4) Attach connectors, electrolytic capacitors, etc.
to PWB, taking care that all connections are
tight.
5) Be sure to use specified components where
high precision is required.
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