JVC AV-27750 User manual

SERVICE MANUAL
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CONTENTS
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SPECIFIC
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No.51127
COPYRIGHT © 1996 VICTOR COMPANY OF JAPAN,LTD. June 1996

AV-27750 |
SPECIFICATIONS
Dimensions (W XH xD) 25-7/8” X 23-1/8” X 20-1/2” / 65.50m X 58.6cm X 51.8em
Mass
Tv System and Color system
TV RF System
Color System
Sound System
TV Receiving Channels and Frequency
VL Band
VH Band
UHF Band
CATV Receiving Channels and
Frequency (Quartz Synthesizer system)
Low Band
High Band
Mid Band
Super Band
Hyper Band
ULTRA Band
Sub Mid Band
TV/CATV Total Channel
Intermediate Frequency
Video IF Carrier
Sound IF Carrier
Color Sub Carrier
Antenna terminal
Power Input
Power Consumption
Input Current
Picture Tube :
Viewable Picture Size (W xH)
High Voltage
Speaker
Audio Power Output
Input (1, 2 )
73.3lbs / 33.3kg
CCIR (M)
NTSC
BTSC (Multi Channel Sound)
(02 ~ 06) 54MHz ~ 88MHz
(07 ~ 13) 174MHz ~ 216MHz
(14 ~ 69) 470MHz ~ 806MHz
(02 ~ 06, A-8) by (02 ~ 06&01)
(07 ~ 13) by (07 ~ 13)
(A ~ 1) by (14 ~ 22)
(J ~ W) by (23 ~ 36)
(W+1 ~ W+28) by (37 ~ 64)
(W +29 ~ W+84) by (65 ~ 125)
(A8, A4 ~ A1) by (01, 96 ~ 99)
180 Channels
45.75MHz
41.25MHz (4.5MHz)
3.58MHz
75Q (VHF/UHF) Terminal, F-Type Connector
120V AC, 60Hz
120W(US)
1.5A(CA)
27”(69cm) measured diagonally, Full Square
21-5/16” X 16” / 54.1cm x 40.6cm
30kV +1.3kV (at zero beam current )
2” X 4-3/4” /5X 12cm Oblong Type x2
SW x2
Video : 1 Vp-p 752 (RCA pin jack)
(54MHz~ 804MHz)
Audio : 500 mV rms (-40Bs), High Impedance (RCA pin jack)
Y : 1 Vp-p positive (negative sync provided,when terminated with 752)
C : 0.286 Vp-p ( burst signal, when terminated with 752)
Variable: More than 0~ 1550mV rms ( + 6dBs)
Low Impedance (400Hz when modulated 100%) (RCA pin jack)
Fix: 500 mV rms (-4dBs)
Low Impedance (400Hz when modulated 100%) (RCA pin jack)
RECEIVER / AMP : 3.5mm mini jack
VCR ONLY : 3.5mm mini jack
S-VIDEO IN
Variable / Fix Audio Output
AV Compulink Input
Remote Control Unit RM-C742-1C (AA/R6/UM-3 dry battery x 2)
Design & specification subject to change without notice.
2 (No.51127)

SAFETY PRECAUTIONS
The design of this product contains special hardware, many circuits
and components specially for safety purposes. For continued pro-
tection,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.
Alterations of the design or circuitry of the products should not be
made. Any design alterations or additions will void the manufactur-
er’s warranty and will further relieve the manufacturer of responsi-
bility for personal injury or property damage resulting therefrom.
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 fea-
tures are identified by shading on the schematics and by
(A) 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 Ser-
vice manual may cause shock, fire, or other hazards.
Use isolation transformer when hot chassis.
The chassis and any sub-chassis contrained in some products are
connected to one side of the AC power line. An isolation transform-
er 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.
Don’t short between the LIVE side ground and !ISOLAT-
ED(NEUTRAL) side ground or EARTH side ground when re-
pairing.
Some model's power circuit is partly different in the GND. The dif-
ference of the GND is shown by the LIVE : (L) side GND, the ISO-
LATED(NEUTRAL) : (rr) 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 measur-
ing apparatus (oscilloscope etc.) the LIVE side GND and !SOLAT-
ED(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.
if any repair has been made to the chassis, it is recommended that
the B, setting should be checked or adjusted (See ADJUSTMENT
OF B,; POWER SUPPLY).
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 dam-
age, therefore operation under excessive high voltage conditions
should be kept to a minimum, or should be prevented. If severe ar-
cing 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 volt-
age circuitry including the picture tube must be the exact replace-
ments or alternatives approved by the manufacturer of the com-
plete product. :
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 10kQ 2W resistor to the anode button.
When service is required, observe the original lead dress. Extra pre-
caution should be given to assure correct lead dress in the high
voltage circuit area. Where a short circuit has occurred, those com-
ponents that indicate evidence of overheating should be replaced.
Always use the manufacturer's replacement components.
10.
(1)
(2)
11.
| AV-27750
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, vid-
eo/audio input and output terminals, Control knobs,metal cabinet,
screwheads, earphone jack, control shafts, etc.) to be sure the prod-
uct is safe to operate without danger of electrical shock.
Dielectric Strength Test
The isolation between the AC primary circuit and ail metal parts ex-
posed to the user, particularly any exposed metal part having a re-
turn 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 rat-
ed 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.
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.).
e 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 hav-
ing 1000 ohms per volt or more sensitivity in the following manner.
Connect a 150022 10W resistor paralleled by a 0.15yF AC-type ca-
pacitor between an exposed metal part and a known good earth
ground (water pipe, etc.). Measure the AC voltage across the resis-
tor with the AC voltmeter. Move the resistor connection to each ex-
posed metal part, particularly any exposed metal part having a re-
turn path to the chassis, and measure the AC voltage across the re-
sistor. Now, reverse the plug in the AC outlet and repeat each mea-
surement. Any voltage measured must not exceed 0.35V AC
(r.m.s.). This corresponds to 0.5mA AC (r.m.s.).
AC VOLTMETER
(HAVING 10002/V,
OR MORE SENSITIVITY)
PLACE THIS PROBE
ON EACH EXPOSED
METAL PART
15002 10W
GOOD EARTH GROUND
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 voitage hold down circuit”.
This mark shows a fast operating fuse, the letters indicated
below show the rating.
(No.51127) 3

AV-27750 |
FEATURES
@ New chassis design enables use of a main board with
simplified circuitry.
® Comb filter improved picture quality.
® Provided with miniature tuner (TV / CATV)
@ Full-square CRT (cathode ray tube) reproduces fine textured
Closed-caption broadcasts can be viewed.
With AUDIO. VIDEO INPUT terminal.
S-VIDEO input terminal for taking best advantage of Super
VHS.
Variable audio output terminal.
picture in every detail. ® Built-in PIP system.
@ PLL synthesizer system TV / CATV totaling 180 channels. ® An auto demonstration function demonstrates the features of
® AV COMPU LINK terminals allow simultaneous mode this model.
switching of the TV, connected receiver (or amplifier) and/or @ (2C bus control utilizes single chip ICs.
VCR.
DIFFERENCE LIST OF MAIN PARTS
Teco deed
a
AV-27750(US) AV-27750(CA)
cs
4 (No.51127)

| AV-27750
SPECIFIC
SERVICE
INSTRUCTIONS
REPLACEMENT
OF
CHIP
COMPONENT
HCAUTIONS
1. Avoid heating for more than 3 seconds.
2.
Do
not
rub
the
electrodes
and
the
resist
parts
of
the
pattern.
3.
When
removing
a
chip
part,
melt
the
solder
adequately.
4. Do not reuse a chip part after removing it.
SOLDERING IRON
4. Use a high insulation soldering iron with a thin pointed end of it
2.
A
30w
soldering
iron
is
recommended
for
easily
removing
parts.
MREPLACEMENT STEPS
1. How to remove Chip parts
eResistors, capacitors, etc
(1)
As
shown
in
the
figure,
push
TWEEZERS
(2)
Shift
with
tweezers
and
remove
the
part
with
tweezers
and
the
chip
part.
TWEEZERS
alternately
melt
the
solder
at
Q
each end.
ae am
Transistors, diodes, variable resistors, etc
(1)
Apply
extra
solder
to
each
(2)
As
shown
in
the
figure,
push
the
lead.
part
with
tweezers
and
alternately
melt
the
solder
at
each
lead.
Shift
and
remove
the
chip part.
TWEEZERS
SOLDER
Note:
After
removing
the
part,
remove
remaining
solder
from
the
pattern.
2. How
to
install
Chip
parts
Resistors,
capacitors,
etc
(1)
Apply
solder
to
the
pattern
(2)
Grasp
the
chip
part
with
as
indicated
in
the
figure.
tweezers
and
place
it
on
the
TWEEZER
solder.
Then
heat
and
melt
the
solder
at
both
ends
of
the
chip
part.
eTransistors, diodes, variable resistors, etc
(1)
Apply
solder
to
the
(2)
Grasp
the
chip
part
with
(3)
First
solder
lead
A
as
(4)
Then
solder
leads
B
and
C.
pattern
as
indicated
in
the
tweezers
and
place
it
on
indicated
in
the
figure.
figure.
the
solder.
(A) {B) (@)
(C) (C)
(No.51127) 5

AV-27750 |
DISASSEMBLY PROCEDURE
REMOVING THE REAR COVER
1. Unplug the power supply cord.
2. Remove the nine screws marked ® as shown in Fig. 2.
* When reinstalling the rear cover, carefully push it inward after
inserting the chassis into the rear cover groove.
REMOVING THE CHASSIS
.@ After removing the rear cover.
1. Slightly raise the both sides of the chassis by hand and
remove the two claws under the both sides of the chassis from
the front cabinet.
2. Draw the chassis backward along the rail in the arrow direction
marked as shown in the Fig. 2.
(If necessary, take off the wire clamp, conneciors eic.)
@ When conducting a check with power supplied, be sure to
confirm that the CRT earth wire is connected to the CRT
SOCKET PWB and the MAIN PWB.
REMOVING THE FRONT CONTROL PW BOARD
e After removing the rear cover and chassis.
1. Remove the 2 screws marked © as shown in Fig. 2.
2. Remove the FRONT CONTROL PW BOARD toward you.
REMOVING THE TERMINAL BOARD
@ After removing the rear cover.
1. Remove the 4 screws marked © as shown in Fig. 2.
2. After removing the claw marked ©) from the AV JACK PWB
in the direction of arrow mark as shown in Fig.1, remove the 2
claws marked © in the direction of arrow mark, then take off
the TERMINAL BOARD in the direction of arrow marked ©.
REMOVING THE ANT SPLITTER
1. Remove a screw marked ) as shown Fig.1.
CHECKING THE MAIN PW BOARD
1. To check the back side of the MAIN PW Board.
1) Pull out the chassis. (Refer to REMOVING THE
CHASSIS). ;
2) Erect the chassis vertically so that you can easily check the
back side of the MAIN PW Board.
[CAUTION]
@ When erecting the chassis, be careful so that there will be no
contacting with other PWB.
© Before turning on power, make sure that the wire connector,
CRT earth wire and other connectors properly connected.
6 (No.51127)
WIRE CLAMPING AND CABLE TYING
1. Be sure to clamp the wire.
2. Never remove the cable tie used for tying the wires together.
Should it be inadvertently removed, be sure to tie the wires
with a new cable tie.
AV JACK PWB
MAIN PWB
Fig.

| AV-27750
FRONT CABI.
CRT SOCKET PWB
FRONT CONTROL PWB
REAR COVER
AV JACK PWB
(No.51127) 7

AV-27750 |
MEMORY
IC
REPLACEMENT
1. Memory IC
This
model
uses
a
memory
(EEP-ROM)
IC.
The
memory
IC
stores
data
for
proper
operation
of
the
video
and
deflection
circuits.
When
replacing,
be
sure
to
use
an
IC
containing
this
(initial
value)
data.
2.
Memory
IC
replacement
procedure
Screen display
Procedure
(1) Power off
Switch
off
the
power
and
disconnect
the
power
cord
from
the
outlet.
Replace the memory IC.
Initial
value
must
be
entered
into
the
new
IC.
(3) Power on
Connect
the
power
cord
to
the
outlet
and
switch
on
the
power.
(4)
System
constant
check
and
setting
1)
Simultaneously
press
the
DISPLAY
key
and
VIDEO
STATUS
key
of
__
the
remote
control
unit.
2)
The
SERVICE
MENU
screen
of
Fig.
1
is
displayed.
3)
While
the
SERVICE
MENU
is
displayed,
again
simultaneously
press
the
DISPLAY
and
VIDEO
STATUS
keys
to
display
the
Fig.
2
SYSTEM
CONSTANT
screen.
Refer
to
the
SYSTEM
CONSTANT
table
and
check
the
setting
items.
Where
these
differ,
select
the
setting
item
with
the
MENU
UP
|
DOWN
key
and
adjust
the
setting
with
the
MENU
LEFT
/
RIGHT
SERVICE MENU
PICTURE
THEATER OTHERS
PIP
LOW LIGHT HIGH LIGHT
RF AFG 1 RF AFC 2
4
~
z
:
f
l2G
BUS
CTRL
keys.(The
letters
of
the
selected
item
are
displayed
in
yellow.)
5)
After
adjusting,
release
the
MENU
LEFT
/
RIGHT
key
to
store
the
getting
value:
OPERATE
BY[4][*]
Exit
BY
@
Press
the
EXIT
key
twice
to
return
the
normal
screen.
Fig.
1
SYSTEM CONSTANT
AV-27750
(5) Receive channel setting
Refer
to
the
OPERATING
INSTRUCTIONS(USER’S
GUIDE)
and
set
the
receive
channels
(Channels
Preset)
as
described.
YES
User settings
Check
the
user
setting
items
According
to
Table
2.
Where
these
do
not
agree,
refer
to
the
OPERATING
INSTRUCTIONS(USER'S
GUIDE)
and
set
the
items
as
described.
setect By[ally]
OPERATE BY[4][*] exit BY
@
SERVICE MENU setting
Verify
what
to
set
in
the
SERVICE
MENU,
and
set
whatever
is
necessary.
(Fig.
1)
refer
to
the
SERVICE
ADJUSTMENT
for
setting.
8 (No.51127)

TABLE 1 (System Constant setting)
| CCSC¢ttingeconstant constant [| _—s—_Settingvalue value
AV-27730 —> AV-27750 —> AV-27770
AV-32720 —> AV-32730 —> AV-32750 =I
AV-32770 —> AV-35750 —> AV-35770
TABLE 2 (User setting)
Setting Value | Setting tem | Setting Value
1. Use remote controller
keys
POWER
CHANNEL
VOLUME
Tv / VIDEO
CLOSED CAPTION
HYPER SURROUND
2. Settings from MENU
TINT
COLOR
PICTURE
BRIGHT
DETAIL
NOTCH
NOISE MUTE
SET VIDEO STATUS
BASS
TREBLE
BALANCE
MTS
SET CLOCK
ON / OFF TIMER
SET LOCK CODE
OFF
CH - 02
Proper sound volume
TV
OFF (CC1/ 71)
OFF
CENTER
CENTER
CENTER
CENTER
CENTER
OFF
ON
CENTER
CENTER
CENTER
CENTER
STEREO
Unnecessary to set
NO
Unnecessary to set
DISPLAY
VIDEO STATUS
SLEEP TIMER
PIP SOURCE
PIP POSITION
TV SPEAKER
AUDIO OUT
LANGUAGE
CLOSED CAPTION
AUTO TUNER SET UP
CHANNEL SUMMARY
TUNER MODE
AUTO DEMO
AV-27750
| AV-27750
OFF
STANDARD
00
CH - 02
Lower left
ON
FIX
ENG
CAPTION : CC1
TEXT :74
OTHERS
Set optionally
Stations o2 —
04 —
07 —
AIR
Unnecessary to set
(No.51127) 9

AV-27750 |
SERVICE
ADJUSTMENTS
ADJUSTMENT
PREPARATION:
1.
2.
3.
4
5
6.
z
You
can
make
the
necessary
adjustments
for
this
unit
with
either
the
Remote
Control
Unit
or
with
the
adjustment
tools
and
parts
as
before.
Adjustment
with
the
Remote
Control
Unit
is
made
on
the
basis
of
the
initial
setting
values;
however,
the
new
setting
values
which
set
the
screen
to
its
optimum
condition
may
differ
from
the
initial
settings.
Turn
on
the
power
for
the
set
and
test
equipment
before
use,
and
start
the
adjustment
procedures
after
waiting
at
least
30
minutes.
_
Make
sure
that
AC
power
is
turned
on
correctly.
Unless
otherwise
specified,
prepare
the
most
suitable
reception
or
input
sigrial
for
adjustment.
Never
touch
any
adjustment
parts
which
are
not
specified
in
the
list
for
this
adjustment
-
variable
resistors,
transformers,
condensers,
etc.
.
Presetting
before
adjustment.
Unless
otherwise
specified
in
the
adjustment
instructions,
preset
the
following
functions
with
the
Remote
Control
Unit:
CENTER
TESTERS
&
TOOLS
ADJUSTMENT
ITEMS
4.
DC
voltmeter
(or
digital
voltmeter)
|
Adjustment
noms
|
Adjustment
items
2.
Oscilloscope
3.
Signal
generator
(Pattern
generator)
[
WHITE
BALANCE
(Low
Light)
_
|
PIP
CIRCUIT
(7
ITEMS)
ITSO
[WHITE
BALANCE
(igh
Gon)
[MTS
NPUT
LEVEL
check
|
it
a
CBSO
OREN:
|
SUB
BRIGHT
|
MTs
STEREO
VCO
5.
TV
audio
multiplex
signal
generator
6.
Frequency
counter
[Focus
||
SUB
CONTRAST
|
MTS
SAP
VCO
V.
CENTER,
V.
SIZE
SUB
COLOR
MTS
FILTER
check
and
V.POSITION
:
H.
POSITION
|
sus
TINT
|
MTS
SEPARATION
POWER VOL cH MENU
ADJUSTMENT
LOCATIONS
|
FRONT lf H
FRONT
2
2—
gm
i
oa
hes 15) ;
MAIN
PWB
ASS‘'Y
FRONT
CONTROL
PWB
ASS'Y
(SOLDER
SIDE)
Bjc=7
(c704 q
(C702
TOP
(SOLDER SIDE) ap
F9O1(5A)
PEO
CRT EARTH
(BRAIDED ASS'Y}
CRT SOCKET PWBASS'Y
UPPER : FOCUS
—- LOWER : SCREEN
CRTEARTH
{BRAIDED ASS'Y}
10 (No.51127)