Zenith L20V36 Series, Service Manual

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PRODUCT SAFETY
IMPORTANT SAFETY NOTICE
This manual was prepared for use only by properly trained audiovisual 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’s 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 Electrostatically Sensitive
(ES) Devices. Examples of typical ES devices are integrated circuits and some
field-effect transistors and semiconductor “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, obtain and wear a
commercially available discharging wrist strap device, 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 removal 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 electrical charge
sufficient to damage ES devices.
6. Do not remove a replacement ES device from its protective package until
immediately before you are ready to install it. (Most replacement ES devices
are packaged with leads electrically shorted together by conductive foam,
aluminum foil, or comparable conductive 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 installed.
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 replacement 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; Increase 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
experienced 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