SAFETY PRECAUTIONS
WARNING: The chassis of this receiver has a floating ground with the
potential of one half the AC line voltage in respect to earth ground.
Service should not be attempted by anyone not familiar with the
precautions necessary when working on this type of equipment.
The following precautions must be observed:
1. An isolation transformer must be connected in the power line
between the receiver and the AC line before any service is
performed on the receiver.
2. Comply with all caution and safety-related notes provided on the
side of the cabinet, inside the cabinet, on the chassis, and the
picture tube.
3. When replacing a chassis in the cabinet, always be certain that all
the protective devices are installed properly, such as control
knobs, adjustment covers, shields and barriers.
4. Before replacing the back cover of the set, thoroughly inspect the
inside of the cabinet to see that no stray parts or tools have been
left inside.
Before returning any television to the customer, the service
technician must perform the following safety checks to be sure
that the unit is completely safe to operate without danger of
electrical shock.
ANTENNA COLD CHECK
Remove AC plug from the 120 VAC outlet and place a jumper
across the two blades. Connect one lead of an ohmmeter to the
jumpered AC plug, and touch the other lead to each exposed antenna
terminal (UHF and VHF antenna terminals). The resistance must
measure between 1M ohm and 5.2M ohm. Any resistance value
below or above this range indicates an abnormality which requires
corrective action.
LEAKAGE CURRENT CHECK
P
lug the AC line cord directly into a 120 VAC outlet. (Do not use an
isolation transformer for this check.) Use an AC voltmeter, that has
5000 ohms per volt or more sensitivity. Connect a 1500 ohm 10 watt
resistor, paralleled by a 0.15 µF 150 VAC capacitor, between a
known good earth ground (water pipe, conduit, etc.) and all
exposed metal parts of the cabinet (antennas, handle bracket, metal
cabinet, screw heads, metal overlays, control shafts, etc.). Measure
the AC voltage across the 1500 ohm resistor. The AC voltage should
not exceed 750 mV. A reading exceeding 750 mV indicates that a
dangerous potential exists. The fault must be located and correct-
ed. Repeat the above test with the receiver power plug reversed.
NEVER RETURN A RECEIVER TO THE CUSTOMER WITHOUT
TAKING THE NECESSARY CORRECTIVE ACTION.
PRODUCT SAFETY NOTICE
W
hen replacing components in a receiver, always keep in mind
the necessary product safety precautions. Pay special attention
to the replacement of components marked with a
in the parts
list and in the schematic diagrams. To ensure safe product oper-
ation, it is necessary to replace those components with the exact
same PART
S.
X-RADIATION PRECAUTION
The primary source of X-RADIATION in solid-state receivers is the pic-
ture tube. The picture tube is specially constructed to limit X-Ray
emission. For continued X-RADIATION protection, the replacement
tube must be the same type as the original (including the suffix letter in
the part numbers). Excessive high voltage may produce potentially
hazardous X-RADIATION. To avoid such hazards, the high voltage must
be maintained within specific limits. Refer to the X-RADIATION WARN-
ING NOTE on the CHASSIS SCHEMATIC in this service manual for
specific high voltage limits. If the high voltage exceeds specified limits,
check the components specified on the chassis schematic diagram
and take the necessary corrective action. Carefully follow the instruc-
tions for the +B Voltage Check and the High Voltage Check to maintain
the high voltage within the specified limits.
HIGH VOLTAGE HOLD-DOWN TEST
To prevent X-RADIATION from the picture tube due to excessive
high voltage, a HOLD-DOWN circuit is provided in the high voltage
circuit. Every time the receiver is serviced, the high voltage HOLD-
DOWN circuit must be tested for proper operation. Refer to the
HIGH VOLTAGE HOLD-DOWN TEST in service adjustments.
SERVICING ELECTROSTATICALLY SENSATIVE DEVICES
Semiconductors (solid-state devices) that can be damaged by static
electricity are referred to as Electrostatically Sensitive (ES) devices.
Examples of typical ES devices are: Integrated Circuits (IC), Field-
Effect Transistors (FET), and “chip” components. The following
techniques should be observed strictly, to reduce the occurrence of
semiconductor damage due to electrostatic discharge.
1. Immediately prior to handling any semiconductor component or
an assembly containing a semiconductor device or devices, dis-
charge the electrostatic buildup on your body by touching a
known earth ground. You may also obtain and wear a commer-
cially available discharging wrist strap device.
CAUTION: Be sure to remove the wrist strap before applying
power to any unit being serviced.
2. After removing an ES equipped assembly, place it on a conduc-
tive surface, such as, aluminum foil, to prevent buildup or
exposure to static electricity.
3. Use only grounded-tip soldering irons to solder or unsolder ES
devices.
4. Use only anti-static solder removal devices. Some suction-type
devices can generate static electricity adequate to damage ES
devices.
5. A replacement ES device will come packaged in protective material
(conductive foam, aluminum foil, or some comparable conductive
material). Do Not remove an ES device from its protective packag-
ing unless you are prepared to install it immediately.
6. Precisely prior to removing an ES device from its protective pack-
aging, touch the protective packaging to the chassis or
assembly in which the device will be install
ed.
CAUTION: Be sure that no power is applied to the chassis or circuit
assembly.
7. Incidental body movements, such as, lifting a foot from a carpeted
floor or the rubbing of fabric together can generate static electricity
sufficient to damage ES devices. Therefore, minimize all body
movements while handling exposed (unpackaged) ES devices.
— 2 —
SAFETY INSTRUCTIONS
0.15 μF 150V AC
1500 ohm
10 watt
Good earth ground
such as a water pipe,
conduit, etc.
AC OUTLET
TELEVISION
RECEIVER
READING SHOULD NOT EXCEED 750 mV.
AC VOLTMETER
(5000 ohms per volt or more sensitivity)
To be touched to all of exposed metal parts.
Voltmeter Hook-up for Leakage Current Check.
