Zenith L20V26 Seroes, Service Manual

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CM154 - 923-03488
2
L20V26 - SAFETY
PRODUCT SAFETY
IMPORTANT SAFETY NOTICE
This manual was prepared for use only by properly trained audio-
visual service technicians. When servicing this product, under no
circumstances should the original design be modified or altered
without permission from Zenith Electronics Corporation. All
components should be replaced only with types identical to those
in the original circuit and their physical location, wiring, and lead
dress must conform to original layout upon completion of repairs. If
any fuse (or Fusible Resistor) in this TV receiver is blown, replace it
only with the factory specified fuse type and rating. When replacing
a high wattage resistor (Oxide Metal Film Resistor, over 1W), keep the
resistor 10mm away from PCB. Always keep wires away from high
voltage or high temperature parts.
Special components are also used to prevent shock and fire hazard.
These components are indicated by the letter “x” included in their
component designators and are required to maintain safe
performance. No deviations are allowed without prior approval by
Zenith Electronics Corporation. Service work should be performed
only after you are thoroughly familiar with these safety checks and
servicing guidelines.
Circuit diagrams may occasionally differ from the actual circuit used.
This way, implementation of the latest safety and performance
improvement changes into the set is not delayed until the new
service literature is printed.
CAUTION: Do not attempt to modify this product in any way. Never
perform customized installations without manufacturer’s approval.
Unauthorized modifications will not only void the warranty, but
may lead to property damage or user injury.
GENERAL GUIDANCE
An lsolation Transformer should always be used during the servicing
of a receiver whose chassis is not isolated from the AC power line. Use
a transformer of adequate power rating to protect against personal
injury from electrical shocks. It will also protect the receiver and its
components from being damaged by accidental shorts of the circuitry
that may be inadvertently introduced during the service operation.
Before returning the receiver to the customer, always perform an AC
leakage current check on the exposed metallic parts of the cabinet,
such as antennas, terminals, etc., to be sure the set is safe to operate
without damage of electrical shock.
LEAKAGE CURRENT COLD CHECK (ANTENNA COLD CHECK)
With the instrument AC plug removed from AC source, connect an
electrical jumper across the two AC plug prongs. Place the AC switch
in the on position, connect one lead of ohm-meter to the AC plug
prongs tied together and touch other ohm-meter lead in turn to
each exposed metallic parts such as antenna terminals, phone jacks,
etc. If the exposed metallic part has a return path to the chassis, the
measured resistance should be between 1M
Ω
and 5.2M
Ω
. When the
exposed metal has no return path to the chassis the reading must be
infinite. Any other abnormality that exists must be corrected before
the receiver is returned to the customer.
ELECTROSTATICALLY SENSITIVE DEVICES
Some semiconductor (solid-state) devices can be damaged easily by
static electricity. Such components commonly are called Electro-
statically Sensitive (ES) Devices. Examples of typical ES devices are
integrated circuits and some field-effect transistors and semicon-
ductor “chip” components. The following techniques should be
used to help reduce the incidence of component damage caused by
static electricity.
1. Immediately before handling any semiconductor component or
semiconductor-equipped assembly, drain off any electrostatic charge
on the body by touching a known earth ground. Alternatively, ob-
tain and wear a commercially available discharging wrist strap de-
vice, which should be removed for potential shock reasons prior to
applying power to the unit under test.
2. After removing an electrical assembly equipped with ES devices,
place the assembly on a conductive surface such as an ESD mat, to
prevent electrostatic charge buildup or exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or unsolder ES
devices.
4. Use only an anti-static solder removal device. Some solder re-
moval devices not classified as “anti-static” can generate electrical
charges sufficient to damage ES devices.
5. Do not use freon-propelled chemicals. These can generate electri-
cal charge sufficient to damage ES devices.
6. Do not remove a replacement ES device from its protective pack-
age until immediately before you are ready to install it. (Most re-
placement ES devices are packaged with leads electrically shorted
together by conductive foam, aluminum foil, or comparable con-
ductive material.)
7. Immediately before removing the protective material from the
leads of a replacement ES device, touch the protective material to
the chassis or circuit assembly into which the device will
be in-
stalled.
Caution: Be sure no power is applied to the chassis or circuit, and
observe all other safety precautions.
8. Minimize bodily motions when handling unpackaged replace-
ment ES devices. (Otherwise, seemingly harmless motion, such as the
brushing together of your clothing or the lifting of your foot from a
carpeted floor, can generate static electricity sufficient to damage
an ES device.)
REGULATORY INFORMATION
This equipment has been tested and found to comply with the limits
for a Class B digital device, pursuant to Part 15 of the FCC Rules.
These limits are designed to provide reasonable protection against
harmful interference when the equipment is operated in a residential
installation. This equipment generates, uses and can radiate radio
frequency energy and, if not installed and used in accordance with
the instruction manual, may cause harmful interference to radio
communications. However, there is no guarantee that interference
will not occur in a particular installation. If this equipment does
cause harmful interference to radio or television reception, which
can be determined by turning the equipment off and on, the user is
encouraged to try to correct the interference by one or more of the
following measures: Reorient or relocate the receiving antenna; In-
crease the separation between the equipment and receiver; Connect
the equipment into an outlet on a circuit different from that to
which the receiver is connected; Consult the dealer or an experi-
enced radio/TV technician for help.
The responsible party for this device’s compliance is:
Zenith Electronics Corporation
201 James Record Road
Huntsville, AL 35824, USA
Digital TV Hotline: 1-800-243-0000
PRODUCT SAFETY