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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.
DO NOT OPERATE THIS TELEVISION RECEIVER
WITHOUT THE PROTECTIVE SHIELD IN POSITION AND
PROPERLY SECURED.
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 resis-
tance must measure between 1M ohm and 5.2M ohm. Any
resistance value below or above this range indicates an abnor-
mality 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 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 corrected. Repeat the above test
with the receiver power plug reversed.
NEVER RETURN A RECEIVER TO THE CUSTOMER
WITHOUT TAKING THE NECESSARY CORRECTIVE
ACTION.
X-RADIATION PRECAUTION
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 let-
ter 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 volt-
age 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 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 volt-
age 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 adjust-
ments.
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.
SAFETY INSTRUCTIONS
0.15
µ
F 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.
Содержание DS13310, DS19310
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