Hitachi 42EDT41A Service Manual page 4

CAUTION: Before servicing instruments covered by this service
data and its supplements and addenda, read and follow the
"Important Safety Instructions" on page 3 of this publication.
NOTE: If unforeseen circumstances create conflict between the
following servicing precautions and any of the safety precautions
on page 3 of this publication, always follow the safety
precautions. Remember: Safety First.
General Servicing Guidelines
1. Always unplug the instrument AC power cord from the AC
power source before:
a. Removing or reinstalling any component, circuit board,
module, or any other instrument assembly.
b. Disconnecting or reconnecting any instrument electrical
plug or other electrical connection.
c. Connecting a test substitute in parallel with an electrolytic
capacitor in the instrument.
CAUTION: A wrong part substitution or incorrect polarity
installation of electrolytic capacitors may
result in an explosion hazard.
2. Do not spray chemicals on or near this instrument or any of its
assemblies.
3. Unless specified otherwise in these service data, clean
electrical contacts by applying the following mixture to the
contacts with a pipe cleaner, cotton-tipped stick or
comparable nonabrasive applicator: 10% (by volume)
Acetone and 90% (by volume) isopropyl alcohol (90%-99%
strength).
CAUTION: This is a flammable mixture. Unless specified
otherwise in these service data, lubrication of
contacts is not required.
4. Do not defeat any plug/socket of voltage interlocks with which
instruments covered by this service data might be equipped.
5. Do not apply AC power to this instrument and/or any of its
electrical assemblies unless all solid-state device heat-sinks
are correctly installed.
6. Always connect the test instrument ground lead to the
appropriate instrument chassis ground before connecting the
test instrument positive lead. Always remove the test
instrument ground lead last.
7. Use with this instrument only the test fixtures specified in this
service data.
CAUTION: Do not connect the test fixture ground strap to
any heatsink in this instrument.
TABLE OF CONTENTS
SERVICING PRECAUTIONS
Electrostatically Sensitive (ES) Devices
Some semiconductor (solid state) devices can be damaged
easily by static electricity. Such components commonly are called
Electrostatically Sensitive (ES) Devices. Examples of typical ES
devices are integrated circuits and some field-effect transistors
and semiconductor "chip" components. The following techniques
should be used to help reduce the incidence of component
damage caused by static electricity.
1. Immediately before handling any semiconductor component
or
electrostatic charge on your body by touching a known earth
ground. Alternatively, obtain and wear a commercially
available discharging wrist strap device, which should be
removed for potential shock reasons prior to applying power to
the unit under test.
2. After removing an electrical assembly equipped with ES
devices, place the assembly on a conductive surface such as
aluminum foil, to prevent electrostatic charge buildup or
exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or desolder
ES devices.
4. Use only an anti-static type solder removal device. Some
solder removal devices not classified as "anti-static" can
generate electrical charges sufficient to damage ES device.
5. Do not use freon-propelled chemicals. These can generate
electrical charges sufficient to damage ES devices.
6. Do not remove a replacement ES device from its protective
package until immediately before you are ready to install it.
(Most replacement ES devices are packaged with leads
electrically shorted together by conductive foam, aluminum foil
or comparable conductive material.)
7. Immediately before removing the protective material from the
leads of a replacement ES device, touch the protective
material to the chassis or circuit assembly into which the
device will be installed.
CAUTION: Be sure no power is applied to the chassis or
8. Minimize bodily motions when handling unpackaged
replacement ES devices. (Otherwise harmless motion such as
the brushing together of your clothes fabric or the lifting of your
foot from a carpeted floor can generate static electricity
sufficient to damage an ES device.)
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semiconductor-equipped assembly,
circuit, and observe all other safety precautions.
PW1A
drain off any