Service manual

Operating the receiver outside of its cabinet or with its Before returning the receiver to the user, perform the
back removed involves a shock hazard. Work on following safety checks:
these models should only be performed by those who 1. Inspect all lead dress to make certain that leads are
are thoroughly familiar with precautions necessary not pinched or that hardware is not lodged between
when working on high voltage equipment. the chassis and other metal parts in the receiver.
2. Replace all protective devices such as nonmetallic
Exercise care when servicing this chassis with power control knobs, insulating fishpapers, cabinet backs,
applied. Many B plus and high voltage RF terminals are adjustment and compartment covers or shields,
exposed which, if carelessly contacted, can cause isolation resistor-capacitor networks, mechanical
serious shock or result in damage to the chassis. insulators, etc.
Maintain interconnecting ground lead connections 3. To be sure that no shock hazard exists, a check for
between chassis, escutcheon, picture tube dag and the presence of leakage current should be made at
tuner cluster when operating the chassis. each exposed metal part having a return path to the
chassis (antenna, cabinet metal, screw heads,
These receivers have a "polarized" AC line cord. The AC knobs and/or shafts, escutcheon, etc.) in the
plug is designed to fit into standard AC outlets in one following manner.
direction only. The wide blade connects to the "ground
side" and the narrow blade connects to the "hot side" of Plug the AC line cord directly into a 120V AC receptacle.
the AC line. This assures that the TV receiver is properly (Do not use an Isolation Transformer during these
grounded to the house wiring. If an extension cord must checks.) All checks must be repeated with the AC line
be used, make sure it is of the "polarized" type. cord plug connection reversed. (If necessary, a
nonpolarized adapter plug must be used only for the
Since the chassis of this receiver is connected to one purpose of completing these checks.)
side of the AC supply during operation, service should
not be attempted by anyone not familiar with the If available, measure current using an accurate leakage
IMPORTANT SERVICE SAFETY INFORMATION
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not be attempted by anyone not familiar with the
If available, measure current using an accurate leakage
precautions necessary when working on these types current tester. Any reading of 0.35mA or more is
of equipment. excessive and indicates a potential shock hazard which
must be corrected before returning the receiver to the
When it is necessary to make measurements or tests with owner.
AC power applied to the receiver chassis, an Isolation
Transformer must be used as a safety precaution and to If a reliable leakage current tester is not available, this
prevent possible damage to transistors. The Isolation alternate method of measurement should be used.
Transformer should be connected between the TV line Using two clip leads, connect a 1500 ohm, 10 watt
cord plug and the AC power outlet.
resistor paralleled by a 0.15µF capacitor in series with
a known earth ground, such as a water pipe or conduit
When removing springs or spring mounted parts from the and the metal part to be checked. Use a VTVM or
tuner, tuner cluster or chassis, shatterproof goggles must VOM with 1000 ohms per volt, or higher, sensitivity to
be worn. Keep others without shatterproof goggles away. 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.
TO EXPOSED
METAL PARTS
TO KNOWN
EARTH GROUND
10µF
TEST PROBE
VT VM
AC SCALE
0.15K OHMS
10W
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