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AV-20FD24
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 care-
lessly 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 ! in the 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
No. 52133
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 compart-
ment 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 paral-
leled 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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