Product Safety Servicing Guidelines - Zenith ZVM-121 Service Manual

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PRODUCT SAFETY SERVICING GUIDELINES
CAUTION: Do not attempt to modify any circuit. Per-
form service work only after you are thoroughly
familiar with all of the following safety checks and
servicing guidelines. To do otherwise increases the
risk of potential hazards and injury to the user. CAU-
TION: Never attempt to service a chassis that is con-
nected directly to an AC line. Make sure it is con-
nected through an isolation transformer. No matter
which way the AC plug is inserted, a potential shock
hazard is present at chassis ground unless you use an
isolation transformer during servicing. Since one
side of the AC input is fused; there's a
50%
chance
you'll blow a fuse, or a
50%
chance you'll destroy
components and/or test equipment without an isola-
tion transformer. The chassis consists of a single cir-
cuit board mounted horizontally in the bottom of the
cabinet. All circuit parts are mounted on the board
except the CRT and deflection yoke. The horizontal
sweep transformer is also mounted on the chassis
circuit board. You can slide the board out of the
cabinet without disconnecting it, and the Monitor
will operate with the board exposed. Screws are not
required to hold the board in place. It slides into slots
which are molded into the cabinet, and the cabinet
back holds it in place.
SAFETY CHECKS
After the original service problem has been corrected,
check for the following:
FIRE
&
SHOCK HAZARD
1.
Be sure that all components are positioned in
such a way to avoid the possibility of adjacent
component shorts. This is especially important
on those chassis which are transported to and
from the repair shop.
2.
Never release a repair unless all protective de-
vices such as insulators, barriers, cover shields,
strain reliefs, and other hardware have been
reinstalled per the original design.
3.
Inspect the soldering for possible cold solder
joints, frayed leads, damaged insulation (in-
cluding AC cord), solder splashes or sharp sol-
der points. Remove all loose foreign particles.
4.
Check "across-the-line" capacitors and other
components for physical evidence of damage or
deterioration, and replace them if necessary.
Follow the original layout, lead length, and
dress.
5.
No lead or component should touch a receiving
tube or a resistor rated at
1
watt or more. Avoid
lead tension around protruding metal surfaces.
6.
Always replace critical components (shaded on
the Schematic Diagram and parts lists) such
as: fuses, flameproof resistors, capacitors, etc.
with exact Zenith types. Do not use replacement
components other than those specified or make
unrecommended circuit modifications.