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AV-20FD22
Operating the receiver outside of its cabinet or with its
back removed involves a shock hazard. Work on these
models should only be performed by those who are
thoroughly familiar with precautions necessary when
working on high voltage equipment.
Exercise care when servicing this chassis with power
applied. Many B plus and high voltage RF terminals are
exposed which, if carelessly contacted, can cause
serious shock or result in damage to the chassis.
Maintain interconnecting ground lead connections
between chassis, escutcheon, picture tube dag and
tuner cluster when operating the chassis.
These receivers have a "polarized" AC line cord. The
AC plug is designed to fit into standard AC outlets in one
direction only. The wide blade connects to the "ground
side" and the narrow blade connects to the "hot side" of
the AC line. This assures that the TV receiver is properly
grounded to the house wiring. If an extension cord must
be used, make sure it is of the "polarized" type.
Since the chassis of this receiver is connected to one
side of the AC supply during operation, service should
not be attempted by anyone not familiar with the
precautions necessary when working on these types of
equipment.
When it is necessary to make measurements or tests
with AC power applied to the receiver chassis, an
Isolation Transformer must be used as a safety
precaution and to prevent possible damage to
transistors. The Isolation Transformer should be
connected between the TV line cord plug and the AC
power outlet.
Certain HV failures can increase X-ray radiation.
Receivers should not be operated with HV levels
exceeding the specified rating for their chassis type. The
maximum operating HV specified for the chassis used in
these receivers is 32kV±1.0kV at zero beam current with
a line voltage of 120V AC. Higher voltage may also
increase the possibility of failure in the HV supply.
It is important to maintain specified values of all
components in the horizontal and high voltage circuits
and anywhere else in the receiver that could cause a
rise in high voltage, or operating supply voltages. No
changes should be made to the original design of the
receiver.
Components shown in the shaded areas on the
schematic diagram and/or identified by
replacement parts list should be replaced only with exact
factory recommended replacement parts. The use of
unauthorized substitute parts may create shock, fire, X-
ray radiation, or other hazards.
To determine the presence of high voltage, use an
accurate high impedance HV meter connected between
the second anode lead and the CRT dag grounding
device. When servicing the High Voltage System,
remove static charges from it by connecting a 10k ohm
resistor in series with an insulated wire (such as a test
probe) between the picture tube dag and 2nd anode
lead (have AC line cord disconnected from AC supply).
4
IMPORTANT SERVICE SAFETY INFORMATION
in the
The picture tube used in this receiver employs integral
implosion protection. Replace with a tube of the same
type number for continued safety. Do not lift picture tube
by the neck. Handle the picture tube only when wearing
shatterproof goggles and after discharging the high
voltage completely. Keep others without shatterproof
goggles away.
When removing springs or spring mounted parts from
the tuner, tuner cluster or chassis, shatterproof goggles
must be worn. Keep others without shatterproof goggles
away.
Before returning the receiver to the user, perform the
following safety checks:
1.
Inspect all lead dress to make certain that leads are
not pinched or that hardware is not lodged between
the chassis and other metal parts in the receiver.
2.
Replace all protective devices such as nonmetallic
control knobs, insulating fishpapers, cabinet backs,
adjustment and compartment covers or shields,
isolation resistor-capacitor networks, mechanical
insulators, etc.
3.
To be sure that no shock hazard exists, a check for
the presence of leakage current should be made at
each exposed metal part having a return path to the
chassis (antenna, cabinet metal, screw heads, knobs
and/or shafts, escutcheon, etc.) in the following
manner.
Plug the AC line cord directly into a 120V AC receptacle.
(Do not use an Isolation Transformer during these
checks.) All checks must be repeated with the AC line
cord plug connection reversed. (If necessary, a
nonpolarized adapter plug must be used only for the
purpose of completing these checks.)
If available, measure current using an accurate leakage
current tester. Any reading of 0.35mA or more is
excessive and indicates a potential shock hazard which
must be corrected before returning the receiver to the
owner.
If a reliable leakage current tester is not available, this
alternate method of measurement should be used.
Using two clip leads, connect a 1500 ohm, 10 watt
resistor paralleled by a 0.15µF capacitor in series with a
known earth ground, such as a water pipe or conduit
and the metal part to be checked. Use a VTVM or VOM
with 1000 ohms per volt, or higher, sensitivity to
measure this AC voltage drop across the resistor. Any
reading of 0.35 volt RMS or more is excessive and
indicates a potential shock hazard which must be
corrected before returning the receiver to the owner.
VT VM
AC SCALE
1.5K OHMS
10W
15µF
TO EXPOSED
TEST PROBE
METAL PARTS
TO KNOWN
EARTH GROUND
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