Zenith C34W37 Series Service Manual page 2

PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO-VIDEO PRODUCTS
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.
Special components are also used to prevent x-radiation, 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.
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.
Service work should be performed only after you are thoroughly familiar with
these safety checks and servicing guidelines.
GRAPHIC SYMBOLS
The exclamation point within an equilateral triangle is intended to
alert the service personnel to important safety information in the
service literature.
The lightning flash with arrowhead symbol within an equilateral
triangle is intended to alert the service personnel to the presence
of noninsulated "dangerous voltage" that may be of sufficient
magnitude to constitute a risk of electric shock.
The pictorial representation of a fuse and its rating within an
equilateral triangle is intended to convey to the service personnel
the following fuse replacement caution notice:
CAUTION: FOR CONTINUED PROTECTION AGAINST RISK
OF FIRE, REPLACE ALL FUSES WITH THE SAME TYPE AND
A V
RATING AS MARKED NEAR EACH FUSE.
SERVICE INFORMATION
While servicing, use an isolation transformer for protection from AC line shock.
After the original service problem has been corrected, make a check of the
following:
FIRE AND SHOCK HAZARD
1. Be sure that all components are positioned to avoid a possibility of adjacent
component shorts. This is especially important on items transported to and
from the repair shop.
2. Verify that all protective devices such as insulators, barriers, covers, shields,
strain reliefs, power supply cords, and other hardware have been reinstalled
per the original design. Be sure that the safety purpose of the polarized line
plug has not been defeated.
3. Soldering must be inspected to discover possible cold solder joints, solder
splashes, or sharp solder points. Be certain to remove all loose foreign particles.
4. Check for physical evidence of damage or deterioration to parts and
components, for frayed leads or damaged insulation (including the AC cord),
and replace if necessary.
5. No lead or component should touch a receiving tube or a resistor rated at 1
watt or more. Lead tension around protruding metal surfaces must be avoided.
6. After reassembly of the set, always perform an AC leakage test on all
exposed metallic parts of the cabinet (the channel selector knobs, antenna
terminals, handle and screws) to be sure that set is safe to operate without
danger of electrical shock. DO NOT USE A LINE ISOLATION
TRANSFORMER DURING THIS TEST. Use an AC voltmeter having 5000
ohms per volt or more sensitivity in the following manner: Connect a 1500
ohm, 10 watt resistor, paralleled by a .15 mfd 150V AC type capacitor
between a known good earth ground water pipe, conduit, etc.) and the
exposed metallic parts, one at a time.
Measure the AC voltage across the combination of 1500 ohm resistor and
.15 mfd capacitor. Reverse the AC plug by using a non-polarized adaptor
and repeat AC voltage measurements for each exposed metallic part.
Voltage measured must not exceed 0.75 volts RMS. This corresponds to 0.5
milliamp AC. Any value exceeding this limit constitutes a potential shock
hazard and must be corrected immediately.
Good Earth Ground
such as the Water
Pipe, Conduit, etc.
X-RADIATION
1. Be sure procedures and instructions to all service personnel cover the
subject of x-radiation. The only potential source of x-rays in current TV
receivers is the picture tube. However, this tube does not emit x-rays when
the HV is at the factory-specified level. The proper value is given in the
applicable schematic. Operation at higher voltages may cause a failure of
the picture tube or high-voltage supply and, under certain circumstances,
may produce radiation in excess of desirable levels.
2. Only factory-specified CRT anode connectors must be used.
3. It is essential that the service personnel have available an accurate and
reliable high-voltage meter.
4. When the high-voltage circuitry is operating properly, there is no possibility of
an x-radiation problem. Every time a color chassis is serviced, the brightness
should be run up and down while monitoring the high voltage with a meter, to
be certain that the high voltage does not exceed the specified value and that
it is regulating correctly.
5. When troubleshooting and making test measurements in a product with a
problem of excessively high voltage, avoid being unnecessarily close to the
picture tube and the high voltage power supply. Do not operate the product
longer than necessary to locate the cause of excessive voltage.
6. Refer to HV, B+, and shutdown adjustment procedures described in the
appropriate schematics and diagrams (where used).
IMPLOSION
1. All direct view picture tubes are equipped with an integral implosion
protection system; take care to avoid damage during installation.
2. Use only the recommended factory replacement tubes.
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A.C. Voltmeter
0.15uF
Place this probe
on each exposed
1500 OHM
metal part.
10 WATT