Harman Kardon HD7725 - Electrostatically Sensitive

HD7725
NOTE: If unforeseen circumstances created conflict between
the following servicing precautions and any of the safety
precautions, always follow the safety precautions.
Remember: Safety First.
General Servicing Precautions
a. Always unplug the instrument's AC power cord from the AC
power source before:
(1) Removing or reinstalling any component, circuit board,
module, or any other instrument assembly.
(2) Disconnecting or reconnecting any instrument electrical
plug or other electrical connection.
(3) 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.
b. Do not defeat any plug/socket B+ voltage interlocks with
which instruments covered by this manual might be equipped.
c. 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.
d. Always connect a test instrument’s ground lead to the
instrument chassis ground before connecting the test
instrument positive lead. Always remove the test instrument
ground lead last.
NOTE: Refer to Safety Precautions on Page 2.
(1) The service precautions are indicated or printed on the
cabinet, chassis or components. When servicing, follow the
printed or indicated service precautions and service materials.
(2) The Components used in the unit has a specified
conflammability and dielectric strength. When replacing any
components, use components which has the same ratings.
Components marked ( A\ ) in the circuit diagram are
important for safety or for the characteristics of the unit.
Always replace with the appointed components.
3
An insulation tube or tape is sometimes used and some
components are raised above the printed wiring board for
safety. The internal wiring is sometimes clamped to prevent
contact with heating components. Install them as they were.
(4) After servicing, always check that the removed screws,
components and wiring have been installed correctly and that
the portion around the service part have not been damaged
and so on. Further check the insulation between the blades
of attachment plug and accessible conductive parts.
Insulation Checking Procedure
Disconnect the attachment plug from the AC outlet and turn the
power on. Connect the insulation resistance meter (500V) to
the blades of the attachment plug. The insulation resistance
between each blade of the attachment plug and accessible
conductive parts (Note 1) should be more than 1M-ohm.
NOTE: Accessible Conductive Parts including Metal panels,
Output jacks, etc.
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 sofder or unsolder
ES devices.
4, Use only an anti-static 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 charge 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 alt other safety precautions.
8. Minimize bodily motions when handling unpackaged
replacement ES devices. (Otherwise harmless motion such
as the brushing together or your clothes fabric or the lifting
of your foot from a carpeted floor can generate static
electricity sufficient to damage an ES device.)