JVC AV-20220/S, Service Manual

Page: 3 / 54

No. 51783
C-13210
C-13211
3
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 products 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 necessarily 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 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. Use isolation transformer when hot chassis.
The chassis and any sub-chassis contained in some products
are connected to one side of the AC power line. An isolation
transformer of adequate capacity should be inserted between
the product and the AC power supply point while performing
any service on some products when the HOT chassis is
exposed.
5. Don't short between the LIVE side ground and ISOLATED
(NEUTRAL) side ground or EARTH side ground when
repairing.
Some model's 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 measure 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 will not be kept, a fuse or any parts will be broken.
6. 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).
7. The high voltage applied to the picture tube must conform with
that specified in Service 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 a minimum, or should be
prevented. If severe arcing occurs, remove the AC power
immediately and determine the cause by visual inspection
(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.
11. 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.
9. When service is required, observe the original lead dress.
Extra precaution should be given to assure correct lead dress
in the high voltage circuit area. Where a short circuit has
occurred, those components that indicate evidence of
overheating should be replaced. Always use the
manufacturer's replacement components.
10. 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, video/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
1100V 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 known good
earth ground (water pipe, etc.). Any leakage current must not
exceed 0.5mA AC (r.m.s.).
However, in tropical area, this must not exceed 0.2mA 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 each
measurement. Any voltage measured must not exceed 0.75V
AC (r.m.s.). This corresponds to 0.5mA AC (r.m.s.).
However, in tropical area, this must not exceed 0.3V AC
(r.m.s.). This corresponds to 0.2mA AC (r.m.s.).
0.15
μ
F AC-TYPE
1500
Ω
10W
GOOD
EARTH
GROUND
PLACE THIS PROBE
ON EACH EXPOSED
METAL PART
AC VOLTMETER
(HAVING 1000
Ω
/V,
OR MORE SENSITIVITY)
11. High voltage hold down circuit check.
After repair of the high voltage hold down circuit, this circuit
shall be checked to operate correctly.
See item "
How to check the high voltage hold down
circuit ".
A V
This mark shows a fast
operating fuse, the
letters indicated below
show the rating.
POWER CORD
REPLACEMENT WARNING.
Connecting the white line side of power
cord to “WHT” character side.