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 ser-
vice is performed on the receiver.
2. Comply with all caution and safety-related notes provid-
ed 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.
DO NOT OPERATE THIS TELEVISION RECEIVER
WITHOUT THE PROTECTIVE SHIELD IN POSITION AND
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 ohm-
meter to the jumpered AC plug, and touch the other lead to
each exposed antenna terminal (UHF and VHF antenna ter-
minals). 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
Plug the AC line cord directly into a 120 VAC outlet. (Do not
use an isolation transformer for this check.) Use an AC volt-
meter, 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 corrected. Repeat the above test with the
receiver power plug reversed.
NEVER RETURN A RECEIVER TO THE CUSTOMER
WITHOUT TAKING THE NECESSARY CORRECTIVE ACTION.
— 2 —
READING SHOULD NOT EXCEED 750 mV.
(5000 ohms per volt or more sensitivity)
To be touched to all of exposed metal parts.
Voltmeter Hook-up for Leakage Current Check.
The primary source of X-RADIATION in solid-state receivers is
the picture 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 WARNING 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 instructions for the +B Voltage Check and the High
Voltage Check to maintain the high voltage within the specified
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.
PRODUCT SAFETY NOTICE
When 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
star ( ) in the parts list and in the schematic diagrams. To
ensure safe product operation, it is necessary to replace
those components with the exact same PARTS.
Good earth ground
such as a water pipe,
0.15 µF 150V AC