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SERVICE PRECAUTIONS
2.1 General Servicing Precautions:
Always unplug the receiver AC power cord from the AC
power source before:
a. Removing or reinstalling any component, circuit board
module or any other receiver assembly.
b. Disconnecting or reconnecting any receiver electrical
plug
or other electrical connection.
c.
Connecting a test substitute in parallel with an
electrolytic
capacitor in the receiver.
CAUTION: A wrong part substitution or incorrect polarity
installation of electrolytic capacitors may result in an
explosion
hazard
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".
3. Do not spray chemicals on or near this receiver or any of
its assemblies.
4. Unless specified otherwise in this service manual, clean
electrical contacts only by applying the following
mixture to the contacts with a pipe cleaner, cotton-
tipped stick or comparable non-abrasive applicator; 10%
(by volume) Acetone and 90% (by volume) isopropyl
alcohol (90%-99% strength)
CAUTION: This is a flammable mixture. Unless specified
otherwise in this service manual, lubrication of contacts
in not required.
5. Do not defeat any plug/socket voltage interlocks with
which receivers covered by this service manual might be
equipped.
6. 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.
7. Always connect the test receiver ground lead to the
receiver chassis ground before connecting the test
receiver positive lead. Always remove the test receiver
ground lead last.
8. Use with this receiver only the test fixtures specified in
this service manual. CAUTION: Do not connect the test
fixture ground strap to any heat sink in this receiver.
2.2
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 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 to prevent 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 aluminium foil, to prevent electrostatic charge build up
or exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or
unsolder 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
devices.
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, aluminium foil or comparable
conductive material).
7. 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 device.)
2.3 General Soldering Guidelines
1. Use a grounded-tip, low-wattage soldering iron and
appropriate tip size and shape that will maintain tip
temperature within the range or 450°F.
2. Use an appropriate gauge of RMA resin-core solder
composed of 60 parts tin/40 parts lead.
3. Keep the soldering iron tip clean and well tinned.
4. Thoroughly clean the surfaces to be soldered. Use a mall
wire-bristle (0.5 inch, or 1.25cm) brush with a metal
handle. Do not use Freon-propelled spray-on cleaners.
5. Use the following unsoldering technique
a. Allow the soldering iron tip to reach normal temperature
b. Heat the component lead until the solder melts.
c. Quickly draw the melted solder with an anti-static,
suction- type solder removal device or with solder braid.
CAUTION: Work quickly to avoid overheating the PCB.
d. Closely inspect the solder area and remove any excess or
splashed solder with a small wire-bristle brush.
2.4 Fuse and Conventional Resistor Removal/Replacement
1. Clip each fuse or resistor lead at top of the circuit board
hollows take.
2. Securely crimp the leads of replacement component
around notch at stake top.
3. Solder the connections.
CAUTION: Maintain original spacing between the replaced
component and adjacent components and the circuit board
to prevent excessive component temperatures.
5
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