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SERVICING PRECAUTIONS
CAUTION: Before servicing instruments covered by this 7. Do not apply AC power to this instrument and/or any of its
service data and its supplements and addenda, read and electrical assemblies unless all solid-state device heat
follow the SAFETY PRECAUTIONS on page 3 of this publi- sinks are correctly installed.
cation. 8. Always connect the test instrument ground lead to the
NOTE: If unforeseen circumstances create conflict between appropriate instrument chassis ground before connect-
the following servicing precautions and any of the safety ing the test instrument positive lead. Always remove the
precautions on page 3 of this publication, always follow the test instrument ground lead last.
safety precautions. Remember: Safety First. 9. Use with this instrument only the test fixtures specified in
this service data.
General Servicing Guidelines CAUTION: Do not connect the test fixture ground strap
1. Always unplug the instrument AC power cord from the AC to any heatsink in this instrument.
power source before:
a. Removing or reinstalling any component, circuit board, Electrostatically Sensitive (ES) Devices
module, or any other instrument assembly. Some semiconductor (solid state) devices can be damaged
b. Disconnecting or reconnecting any instrument elec- easily by static electricity. Such components commonly are
trical plug or other electrical connection. called Electrostatically Sensitive (ES) Devices. Examples of
c. Connecting a test substitute in parallel with an elec- typical ES devices are integrated circuits and some field-
trolytic capacitor in the instrument. effect transistors and semiconductor ?chip? components.
Caution: A wrong part substitution or incorrect po- The following techniques should be used to help reduce the
larity installation of electrolytic capacitors incidence of component damage caused by static electricity.
may result in an explosion hazard. 1. Immediately before handling any semiconductor compo-
d. Discharging the picture tube anode. nent or semiconductor-equipped assembly, drain off any
2. Test high voltage only by measuring it with an appropriate electrostatic charge on your body by touching a known
high voltage meter or other voltage measuring device earth ground. Alternatively, obtain and wear a commer-
(DVM, FETVOM, etc.) equipped with a suitable high volt- cially available discharging wrist strap device, which
age probe. Do not test high voltage by ?drawing an arc.? should be removed for potential shock reasons prior to
The H.V. Distribution Box has an internal 400MQ resistor applying power to the unit under test.
(bleeder resistor) connected from the high voltage to 2. After removing an electrical assembly equipped with ES
ground. After power is removed from the instrument the devices, place the assembly on a conductive surface
high voltage will discharge through the high voltage such as aluminum foil, to prevent electrostatic charge
bleeder resistor. If the tubes have high voltage after buildup or exposure of the assembly.
power is removed, then the bleeder resistor is defective or 3. Useonlyagrounded-tip soldering iron to solder or unsolder
the bleeder ground is disconnected. ES devices.
3. Discharge the picture tube?s anode at any of the R, G, or 4. Use only an anti-static type solder removal device Some
B outputs on the High Voltage distribution box only by (a) solder removal devices not classified as ?anti-static? can
first connecting one end of an insulated clip lead to the generate electrical charges sufficient to damage ES de-
degaussing or kine aquadag grounding system shield at vices.
the point where the picture tube socket ground lead is 5. Do not use freon-propelled chemicals. These can gener-
connected, and then (b) touch the other end of the ate electrical charges sufficient to damage ES devices.
insulated clip lead to the picture tube high voltage distri- 6. Do not remove a replacement ES device from its protec-
bution box R, G, or B output, using an insulating handle to tive package until immediately before you are ready to
avoid personal contact with high voltage. install it. (Most replacement ES devices are packaged
4. Do not spray chemical on or near this instrument or any with leads electrically shorted together by conductive
of its assemblies. foam, aluminum foil or comparable conductive material.)
5. Unless specified otherwise in these service data, clean 7. Immediately before removing the protective material from
electrical contacts by applying the following mixture to the the leads of a replacement ES device, touch the protec-
contacts with a pipe cleaner, cotton-tipped stick or com- tive material to the chassis or circuit assembly into which
parable nonabrasive applicator: 10% (by volume) Ac- the device will be installed.
etone and 90% (by volume) isopropyl alcohol (90%-99% CAUTION: Be sure no power is applied to the chassis
strength). Caution: This is a flammable mixture. Unless orcircuit, andobserveallothersafetyprecau-
specified otherwise in these service data, lubrication of tions.
contacts is not required. 8. Minimize bodily motions when handling unpackaged re-
6. Do not defeat any plug/socket B+ voltage interlocks with placement ES devices. (Otherwise harmless motion such
which instruments covered by this service data might be as the brushing together of yourclothesfabric orthe lifting
equipped. of your foot from a carpeted floor can generate static
electricity sufficient to damage an ES device.)
6 |
ACEC
HITACHI
