Hitachi UT42V702/D8MW, Service Manual, Page: 5 / 90

D8MW
TABLE OF CONTENTS
4
SERVICING PRECAUTIONS
CAUTION: Before servicing instruments covered by this
service data and its supplements and addendum, read and
follow the information in previous pages number 2 and 3 of
this publication.
NOTE:
If unforeseen circumstances create conflict between
the following servicing precautions and any of the safety
precautions on the previous pages 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 ex-
plosion 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 heatsinks
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.
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 semiconductor-equipped assembly, drain off
any 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
circuit, and observe all other safety
precautions.
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.)