Sharp 55R-WP4H, Service Manual

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7
61R-WP5H
55R-WP5H
SERVICING PRECAUTIONS
CAUTION: Before servicing instruments covered by this
service data and its supplements and addenda, read and
follow the SAFETY PRECAUTIONS 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.
d. Discharging the picture tube anode.
2. Test high voltage only by measuring it with an appropriate
high voltage meter or other voltage measuring device
(DVM, FETVOM, etc.) equipped with a suitable high
voltage probe. Do not test high voltage by “drawing an
arc.” The H.V. Distribution Box has an internal 400M
Ω
resistor (bleeder resistor) connected from the high
voltage to ground. After power is removed from the
instrument the high voltage will discharge through the
high voltage bleeder resistor. If the tubes have high
voltage after power is removed, then the bleeder resistor
is defective or the bleeder ground is disconnected.
3. Discharge the picture tube’s anode at any of the R, G, or
B outputs on the H.V. Distribution Box only by (a) first
connecting one end of an insulated clip lead to the
degaussing or kine aquadag grounding system shield at
the point where the picture tube socket ground lead is
connected, and then (b) touch the other end of the
insulated clip lead to the picture tube high voltage
distribution box R, G, or B output, using an insulated
handle to avoid personal contact with high voltage.
4. Do not spray chemicals on or near this instrument or any
of its assemblies.
5. Unless specified otherwise in these service data, clean
electrical contracts 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.
6. Do not defeat any plug/socket B+ voltage interlocks with
which instruments covered by this service data might be
equipped.
7. 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.
8. 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.
9. 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 can 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 charges.