1-2 Servicing
Precautions
WARNING:
First read the-Safety Precautions-section of this manual. If some unforeseen circumstance creates a conflict
between the servicing and safety precautions, always follow the safety precautions.
WARNING:
An electrolytic capacitor installed with the wrong polarity might explode
.
1.
Servicing precautions are printed on the cabinet.
Follow them.
2.
Always unplug the units AC power cord from the
AC power source before attempting to:
(a) Remove or reinstall any component or assembly
(b) Disconnect an electrical plug or connector
(c) Connect a test component in parallel with an
electrolytic capacitor
3.
Some components are raised above the printed
circuit board for safety. An insulation tube or tape
is sometimes used. The internal wiring is sometimes
clamped to prevent contact with thermally hot
components. Reinstall all such elements to their
original position.
4.
After servicing, always check that the screws,
components and wiring have been correctly
reinstalled. Make sure that the portion around the
serviced part has not been damaged.
5.
Check the insulation between the blades of the AC
plug and accessible conductive parts (examples:
metal panels and input terminals).
6.
Insulation Checking Procedure: Disconnect the
power cord from the AC source and turn the power
switch ON. Connect an insulation resistance meter
(500V) to the blades of AC plug.
The insulation resistance between each blade of the
AC plug and accessible conductive parts (see
above) should be greater than 1 megohm.
7.
Never defeat any of the B+ voltage interlocks.
Do not apply AC power to the unit (or any of its
assemblies) unless all solid-state heat sinks are
correctly installed.
8.
Always connect an instrument’s ground lead to the
instrument chassis ground before connecting the
positive lead; always remove the instrument’s
ground lead last.
1-3 Precautions for Electrostatic Sensitive Devices (ESDs)
1.
Some semiconductor (solid state) devices are easily
damaged by static electricity. Such components are
called Electrostatic Sensitive Devices (ESDs);
examples include integrated circuits and some field-
effect transistors. The following techniques will
reduce the occurrence of component damage caused
by static electricity.
2.
Immediately before handling any semiconductor
components or assemblies, drain the electrostatic
charge from your body by touching a known earth
ground. Alternatively, wear a discharging wrist-
strap device. (Be sure to remove it prior to applying
power - this is an electric shock precaution.)
3.
After removing an ESD-equipped assembly, place it
on a conductive surface such as aluminum foil to
prevent accumulation of electrostatic charge.
4.
Do not use Freon-propelled chemicals. These can
generate electrical charges that damage ESDs.
5.
Use only a grounded-tip soldering iron when
soldering or unsoldering ESDs.
6.
Use only an anti-static solder removal device. Many
solder removal devices are not rated as anti-static;
these can accumulate sufficient electrical charge to
damage ESDs.
7.
Do not remove a replacement ESD from its
protective package until you are ready to install it.
Most replacement ESDs are packaged with leads
that are electrically shorted together by conductive
foam, aluminum foil or other conductive materials.
8.
Immediately before removing the protective
material from the leads of a replacement ESD,
touch the protective material to the chassis or
circuit assembly into which the device will be
installed.
9.
Minimize body motions when handling unpackaged
replacement ESDs. Motions such as brushing
clothes together, or lifting a foot from a carpeted
floor can generate enough static electricity to
damage an ESD.
