No.51878
AV21BT7ENS / AV21BT7ENB
AV21BT7EPS / AV21BT7EPB
AV21BT7EES / AV21BT7EEB
4
SAFETY PRECAUTIONS
1. The design of this product contains special hardware many
circuits and components specially for safety purposes. For
continued protection, no changes should be made to the original
design unless authorized in writing by the manufacturer.
Replacement parts must be identical to those used in the original
circuits. Service should be performed by qualified personnel
only.
2. Alterations of the design or circuitry of the product should not be
made. Any design alterations or additions will void the
manufacturer's warranty and will further relieve the manufacturer
of responsibility for personal injury or property damage resulting
therefrom.
3. Many electrical and mechanical parts in the products have
special safety-related characteristics. These characteristics are
often not evident from visual inspection nor can the protection
afforded by them necessary be obtained by using replacement
components rated for higher voltage, wattage, etc. Replacement
parts which have these special safety characteristics are
identified in the Parts List of Service Manual.
Electrical
components having such features are identified by shading
on the schematics and by (
) on the Parts List in the
Service Manual.
The use of a substitute replacement which
does not have the same safety characteristics as the
recommended replacement part shown in the Parts List of
Service Manual may cause shock, fire, or other hazards.
4.
Don’t short between the LIVE side ground and ISOLATED
(NEUTRAL) side ground or EARTH side ground when
repairing.
Some models power circuit is partly different in the GND. The
difference of the GND is shown by the LIVE : (
)
side GND, the
ISOLATED(NEUTRAL) : (
) side GND and EARTH : (
) side
GND. Don’t short between the LIVE side GND and ISOLATED
(NEUTRAL) side GND or EARTH side GND and never
measnure with a measuring apparatus (oscilloscope etc.) the
LIVE side GND and ISOLATED(NEUTRAL) side GND or EARTH
side GND at the same time.
If above note willl not be kept, a fuse or any parts will be broken.
5. If any repair has been made to the chassis, it is recommended
that the B1 setting should be checked or adjusted (See
ADJUSTMENT OF B1 POWER SUPPLY).
6. The high voltage applied to the picture tube must conform with
that specified in Srevice manual. Excessive high voltage can
cause an increase in X-Ray emission, arcing and possible
component damage, therefore operation under excessive high
voltage conditions should be kept to minimum, or should be
preveted. If severe arcing occurs, remove the AC power
immediately and determine the cause by visual inspecton
(incorrect installation, cracked or melted high voltage harness,
poor soldering, etc.). To maintain the proper minimum level of
soft X-Ray emission, components in the high voltage circuitry
including the picture tube must be the exact replacements or
alternatives approved by the manufacturer of the complete
product.
7. Do not check high voltage by drawing an arc. Use a high voltage
meter or a high voltage probe with a VTVM. Discharge the
picture tube before attempting meter connection, by connecting
a clip lead to the ground frame and connecting the other end of
the lead through a 10k
Ω
2W resistor to the anode button.
8. When service is required, observe the original lead dress. Extra
precaution should be given to assure correct lead dress in the
hig voltage circuit area. Where a short curcuit has occurred,
those components that indicate evidence of overheating should
be replaced. Always use the manufacturer’s replacement
components.
9.
Isolation Check
(Safety for Electrical Shock Hazard)
After re-assembling the product, always perform an isolation
check on the exposed metal parts of the cabinet (antenna
terminals, videl/audio input and output terminals, Control knobs,
metal cabinet, screwheads, earphone jack, control shafts, etc.)
to be sure the product is safe to operate without danger of
electrical shock.
(1)
Dielectric Strength Test
The isolation between the AC primary circuit and all metal parts
exposed to the user, particularly any exposed metal part having a
return path to the chassis should withstand a voltage of 3000V
AC(r.m.s.) for a period of one second.
( . . .Withstand a voltage of 1100V AC (r.m.s.) to an appliance
rated up to 120V, and 3000V AC (r.m.s.) to an appliance rated
200V or more, for a period of one second.)
This method of test requires a test equipment not generally found
in the service trade.
(2)
Leakage Current Check
Plug the AC line cord directly into the AC outlet (do not use a line
isolation transformer during this check.). Using a ”Leakage
Current Tester”, measure the leakage current from each exposed
metal part of the cabinet, particularly any exposed metal part
having a return path to the chassis, to a knowm good earth
ground (water pipe, etc.). Any leakege current must not exceed
0.5mA AC(r.m.s.).
●
Alternate Check Method
Plug the AC line cord directly into the AC outlet (do not use a line
isolation transformer during this check.). Use an AC voltmeter
having 1000 ohms per volt or more sensitivity in the following
manner. Connect a 1500
Ω
10W resistor paralleled by a 0.15
μ
F
AC-type capacitor between an exposed metal part and a known
good earth ground (water pipe, etc.). Measure the AC voltage
across the resistor with the AC voltmeter. Move the resistor
connection to each exposed metal part, particularly any exposed
metal part having a return path to the chassis, and measure the
AC voltage across the resistor. Now, reverse the plug in the AC
outlet and repeat earch measurement. Any voltage measured
must mot exceed 0.35V AC (r.m.s.). This corresponds to 0.5mA
AC (r.m.s.).
