Zenith DVB318, Service Manual

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IMPORTANT SAFETY NOTICE
This manual was prepared for use only by properly trained audio-video 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 haz-
ard. These components are indicated by the letter “x” included in their compo-
nent 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 modi-
fications 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 tri-
angle is intended to alert the service personnel to the presence of
noninsulated “dangerous voltage” that may be of sufficient magni-
tude to constitute a risk of electric shock.
The pictorial representation of a fuse and its rating within an equi-
lateral 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
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 fol-
lowing:
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 trans-ported 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 par-
ticles.
4. Check for physical evidence of damage or deterioration to parts and compo-
nents, for frayed leads or damaged insulation (including the AC cord), and
replace if necessary.
5. No lead or component should touch a high current device 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 TRANS-
FORMER 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 metal-
lic 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 consti-
tutes a potential shock hazard and must be corrected immediately.
TIPS ON PROPER INSTALLATION
1. Never install any receiver in a closed-in recess, cubbyhole, or closely fitting
shelf space over, or close to, a heat duct, or in the path of heated air flow.
2. Avoid conditions of high humidity such as: outdoor patio installations where
dew is a factor, near steam radiators where steam leakage is a factor, etc.
3. Avoid placement where draperies may obstruct venting. The customer
should also avoid the use of decorative scarves or other coverings that
might obstruct ventilation.
4. Wall- and shelf-mounted installations using a commercial mounting kit must
follow the factory-approved mounting instructions. A product mounted to a
shelf or platform must retain its original feet (or the equivalent thickness in
spacers) to provide adequate air flow across the bottom. Bolts or screws
used for fasteners must not touch any parts or wiring. Perform leakage tests
on customized installations.
5. Caution customers against mounting a product on a sloping shelf or in a tilt-
ed position, unless the receiver is properly secured.
6. A product on a roll-about cart should be stable in its mounting to the cart.
Caution the customer on the hazards of trying to roll a cart with small cast-
ers across thresholds or deep pile carpets.
7. Caution customers against using extension cords. Explain that a forest of
extensions, sprouting from a single outlet, can lead to disastrous conse-
quences to home and family.
A.C. Voltmeter
1500 OHM
10 WATT
Place this probe
on each exposed
metal part.
Good Earth Ground
such as the Water
Pipe, Conduit, etc.
0.15uF
PRODUCT SAFETY SERVICING GUIDELINES FOR VIDEO PRODUCTS