JVC TH-A25 User manual

SERVICE MANUAL
COPYRIGHT © 2003 VICTOR COMPANY OF JAPAN, LIMITED No.MB143
2003/12
DVD DIGITAL CINEMA SYSTEM
MB143200312 TH-A25
TABLE OF CONTENTS
1 PRECAUTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
2 SPECIFIC SERVICE INSTRUCTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
3 DISASSEMBLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
4 ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-12
5 TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13
Area suffix
US ---------------------- Singapore
UB --------------------- Hong Kong
UW ---------- Brazil,Mexico,Peru
UX ------------------- Saudi Arabia
UG - Turkey,South Africa,Egypt
SOUND
VOLUME
SOURCE
STANDBY
STANDBY/ON
DVD DIGITAL CINEMA SYSTEM TH-A25

1-2 (No.MB143)
SPECIFICATION
Designs & specifications are subject to change without notice.
Center unit (XV-THA25)
Amplifier Front/Center/Rear 30 W per channel, min. RMS, driven into 6 Ωat 1 kHz, with no more than 10% total harmonic
distortion
Subwoofer 55 W, min. RMS, driven into 3 Ωat 100 Hz, with no more than 10% total harmonic distortion
Audio Audio input sensitivity/Impedance (at 1 kHz)
Analog input AUX ("AUDIO IN") 500 mV/47 kΩ
Signal-to-Noise Ratio 68 dB
Digital input* DIGITAL IN (OPTICAL) -24 dBm to -14.5 dBm (700 nm ±50 nm)
* Corresponding to Linear PCM, Dolby Digital, and DTS Digital Surround (with sampling frequency-32 kHz, 44.1 kHz, 48
kHz)
Video Color System NTSC/PAL
Horizontal Resolution 480 lines
Output Level VIDEO OUT (Composite) 1.0 V(p-p)/75 Ω
S-VIDEO (Y):1.0 V(p-p)/75 Ω
(C):0.286 V(p-p)/75 Ω
COMPONENT VIDEO OUT Y 1.0 V(p-p)/75 Ω
PB/PR 0.7 V(p-p)/75 Ω
Tuner Tuning Range FM 87.50 MHz - 108.00 MHz
AM 531 kHz - 1 602 kHz (at 9 kHz intervals)
530 kHz - 1 600 kHz (at 10 kHz intervals)
Usable Sensitivity FM 8.0 dBf (0.9 µV/75 Ω)
AM loop antenna 650 µV/m
General Readable Discs DVD VIDEO, Video CD, Super Video CD, Audio CD, CD-R/RW (Audio CD, Video CD, Super
Video CD, MP3, JPEG), DVD-R/RW (Video format)
Power Requirements AC 110 V - 127 V/220 V - 240 V , Adjustable with the voltage selector, 50 Hz/60 Hz
Power Consumption 110 W (at operation) 2 W (in standby mode)
Dimensions (W ×H ×D) 360 mm ×65 mm ×404 mm
Mass 6.3 kg
Subwoofer (SP-WA25)
Speaker 15 cm Bass-reflex, magnetically shielded
Power Handling Capacity 55 W
Impedance 3 Ω(min)
Frequency Range 30 Hz to 200 Hz
Dimensions (W ×H ×D) 210 mm ×382 mm ×338 mm
Mass 6 kg
Satellite Speakers (SP-XTHA25)
Speaker 8 cm Bass-reflex, magnetically shielded
Power Handling Capacity 30 W
Impedance 6 Ω(min)
Frequency Range 80 Hz to 20 kHz
Dimensions (W ×H ×D) 105 mm ×114 mm ×116 mm
Mass 640 g

(No.MB143)1-3
SECTION 1
PRECAUTION
1.1 Safety Precautions
(1) This design of this product contains special hardware and
many circuits and components specially for safety purpos-
es. 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. Services should be per-
formed by qualified personnel only.
(2) Alterations of the design or circuitry of the product should
not be made. Any design alterations of the product should
not be made. Any design alterations or additions will void
the manufacturers warranty and will further relieve the
manufacture 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 characteris-
tics are often not evident from visual inspection nor can the
protection afforded by them necessarily be obtained by us-
ing replacement components rated for higher voltage, watt-
age, etc. Replacement parts which have these special
safety characteristics are identified in the Parts List of Ser-
vice 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 charac-
teristics as the recommended replacement parts shown in
the Parts List of Service Manual may create shock, fire, or
other hazards.
(4) The leads in the products are routed and dressed with ties,
clamps, tubings, barriers and the like to be separated from
live parts, high temperature parts, moving parts and/or
sharp edges for the prevention of electric shock and fire
hazard. When service is required, the original lead routing
and dress should be observed, and it should be confirmed
that they have been returned to normal, after reassem-
bling.
(5) Leakage shock hazard testing
After reassembling the product, always perform an isola-
tion check on the exposed metal parts of the product (an-
tenna terminals, knobs, metal cabinet, screw heads,
headphone jack, control shafts, etc.) to be sure the product
is safe to operate without danger of electrical shock.Do not
use a line isolation transformer during this check.
• Plug the AC line cord directly into the AC outlet. Using a
"Leakage Current Tester", measure the leakage current
from each exposed metal parts of the cabinet, particular-
ly any exposed metal part having a return path to the
chassis, to a known good earth ground. Any leakage cur-
rent must not exceed 0.5mA AC (r.m.s.).
• Alternate check method
Plug the AC line cord directly into the AC outlet. Use an
AC voltmeter having, 1,000Ωper volt or more sensitivity
in the following manner. Connect a 1,500Ω10W resistor
paralleled by a 0.15µF AC-type capacitor between an ex-
posed metal part and a known good earth ground.
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. Voltage measured any must
not exceed 0.75 V AC (r.m.s.). This corresponds to 0.5
mA AC (r.m.s.).
1.2 Warning
(1) This equipment has been designed and manufactured to
meet international safety standards.
(2) It is the legal responsibility of the repairer to ensure that
these safety standards are maintained.
(3) Repairs must be made in accordance with the relevant
safety standards.
(4) It is essential that safety critical components are replaced
by approved parts.
(5) If mains voltage selector is provided, check setting for local
voltage.
1.3 Caution
Burrs formed during molding may be left over on some parts
of the chassis.
Therefore, pay attention to such burrs in the case of pre-
forming repair of this system.
1.4 Critical parts for safety
In regard with component parts appearing on the silk-screen
printed side (parts side) of the PWB diagrams, the parts that are
printed over with black such as the resistor ( ), diode ( )
and ICP ( ) or identified by the " " mark nearby are critical
for safety. When replacing them, be sure to use the parts of the
same type and rating as specified by the manufacturer.
(This regulation dose not Except the J and C version)
Good earth ground
Place this
probe on
each exposed
metal part.
AC VOLTMETER
(Having 1000
ohms/volts,
or more sensitivity)
1500 10W
0.15 F AC TYPE

1-4 (No.MB143)
1.5 Preventing static electricity
1.5.1 Grounding to prevent damage by static electricity
Electrostatic discharge (ESD), which occurs when static electricity stored in the body, fabric, etc. is discharged, can destroy the laser
diode in the traverse unit (optical pickup). Take care to prevent this when performing repairs.
1.5.2 About the earth processing for the destruction prevention by static electricity
Static electricity in the work area can destroy the optical pickup (laser diode) in devices such as DVD players.
Be careful to use proper grounding in the area where repairs are being performed.
(1) Ground the workbench
Ground the workbench by laying conductive material (such as a conductive sheet) or an iron plate over it before placing the
traverse unit (optical pickup) on it.
(2) Ground yourself
Use an anti-static wrist strap to release any static electricity built up in your body.
1.5.3 Handling the optical pickup
(1) In order to maintain quality during transport and before installation, both sides of the laser diode on the replacement optical pick-
up are shorted. After replacement, return the shorted parts to their original condition. (Refer to the text.)
(2) Do not use a tester to check the condition of the laser diode in the optical pickup. The tester's internal power source can easily
destroy the laser diode.
1.5.4 Handling the traverse unit (optical pickup)
(1) Do not subject the traverse unit (optical pickup) to strong shocks, as it is a sensitive, complex unit.
(2) Remove solder of the short lands on the flexible wire after replacing the optical pickup. For specific details, refer to the replace-
ment procedure in the text. Remove the anti-static pin when replacing the traverse unit.
Be careful not to take too long a time when attaching it to the connector.
(3) Handle the flexible wire carefully as it may break when subjected to strong force.
(4) It is not possible to adjust the semi-fixed resistor that adjusts the laser power. Do not turn it.
1.5.5 Attention when traverse unit is decomposed
*Please refer to "Disassembly method" in the text for the DVD pickup.
• Apply solder to the short circuit points before the flexible wire is disconnected from the connector on the DVD pickup.
(If the flexible wire is disconnected without applying solder, the DVD pickup may be destroyed by static electricity.)
• In the assembly, be sure to remove solder from the short circuit points after connecting the flexible wire.
Conductive material
(conductive sheet) or iron plate
(caption)
Anti-static wrist strap

(No.MB143)1-5
SECTION 2
SPECIFIC SERVICE INSTRUCTIONS
This service manual does not describe SPECIFIC SERVICE INSTRUCTIONS.

1-6 (No.MB143)
SECTION 3
DISASSEMBLY
3.1 Main body section
3.1.1 Removing the top cover
(See Figs.1 and 2)
(1) From the both sides of the main body, remove the four
screws Aattaching the top cover. (See Fig.1)
(2) From the back side of the main body, remove the four
screws Battaching the top cover. (See Fig.2)
(3) Take out the top cover in the upward direction while ex-
tending the lower sections of the top cover in the direction
of right and left.
Fig.1
Fig.2
Top cover
AA
Top cover Rear panel
B

(No.MB143)1-7
3.1.2 Removing the tray door
(See Figs.3 to 6)
• Prior to performing the following procedures, remove the top
cover.
• The following procedures are performed in the case of power
on.
(1) From the front side of the main body, push the disk open
bottom and eject the disc tray. (See Fig.3)
(2) Release the joints ain the upward direction and take out
the tray door. (See Fig.3)
NOTE:
The following procedures are performed in the case of power
off.
(1) From the top side of the main body, remove the four
screws Cattaching the DVD top cover. (See Fig.4)
(2) Take out the disc tray in the direction of the arrow while
lifting the section b. (See Fig.5)
(3) Release the joints ain an upward direction and take out
the tray door. (See Fig.6)
(4) Remove the four screws Dattaching the DVD mecha-
nism assembly. (See Fig.6)
(5) Disconnect the wires from the connectors AJ1, AJS1 and
PCN1 on the DVD mechanism assembly, and take out
the DVD mechanism assembly. (See Fig.6)
(6) Push in the disc tray while lifting the section b. (See
Fig.5)
Reference:
• When pushing in the disc tray, push it until the posi-
tion of the claw c. (See Fig.5)
(7) Attach the DVD top cover with the four screws Cto the
DVD mechanism assembly.
Reference:
• Attaching method of the DVD mechanism assembly
refers to the section 3.1.3.
Fig.3
Fig.4
Fig.5
Fig.6
Joints aDisk open buttonTray door
C
C
DVD
mechanism
assembly
DVD
top cover
Section b
Claws c
DVD mechanism
assembly
Disk tray
Tray door
Joints a
PCN1
AJ1
AJS1
DD
DVD
mechanism
assembly
D

1-8 (No.MB143)
3.1.3 Removing the DVD mechanism assembly
(See Fig.7)
• Prior to performing the following procedures, remove the top
cover and tray door.
(1) From the top side of the main body, remove the four screws
Dattaching the DVD mechanism assembly.
(2) Disconnect the wires from the connectors AJ1, AJS1 and
PCN1 on the DVD mechanism assembly, and take out the
DVD mechanism assembly.
Fig.7
3.1.4 Removing the front panel assembly (See Figs.8 and 9)
• Prior to performing the following procedures, remove the top
cover and tray door.
(1) From the top side of the main body, disconnect the card
wire from the connector UW4 on the function board. (See
Fig.8)
(2) From the bottom side of the main body, remove the four
screws Eattaching the front panel assembly. (See Fig.9)
(3) From the both sides of the main body, remove the two
screws Fattaching the front panel assembly. (See Fig.9)
(4) Release the joints din forward direction and take out the
front panel assembly. (See Fig.9)
3.1.5 Removing the tuner pack
(See Figs.8 and 10)
• Prior to performing the following procedures, remove the top
cover.
(1) From the top side of the main body, disconnect the card
wire from the connector VW4 on video board. (See Fig.8)
(2) Remove the screw Gattaching the tuner pack. (See Fig.8)
(3) From the back side of the main body, remove the screw H
attaching the tuner pack. (See Fig.10)
3.1.6 Removing the fan motor (See Figs.8 and 10)
• Prior to performing the following procedures, remove the top
cover.
(1) From the top side of the main body, disconnect the fan
motor wire from the connector UW9 on the function board.
(See Fig.8)
(2) From the back side of the main body, remove two screws J
attaching the fan motor. (See Fig.10)
Fig.8
Fig.9
Fig.10
DD
DVD
mechanism
assembly
D
AJS1
PCN1
JS1
Joint d
F
E
Front panel assembly
VW4
Front panel assembly UW4
Fan motor UW9 Video board
Tuner
pack
G
Function
board
Fan motor
Rear panel
J H

(No.MB143)1-9
3.1.7 Removing the rear panel
(See Fig.11)
• Prior to performing the following procedures, remove the top
cover and fan motor.
(1) From the back side of the main body, remove the power
cord from the rear panel in the direction of the arrow.
(2) Remove the screw H, two screws K, five screws Lthree
screws Mand attaching the rear panel.
(3) Take out the rear panel.
Fig.11
3.1.8 Removing the video board
(See Fig.12)
• Prior to performing the following procedures, remove the top
cover, fan motor and rear panel.
(1) From the top side of the main body, disconnect the power
cord from the connector ACW1 on the main board.
(2) Disconnect the card wire from the connector VW4 on the
video board.
(3) Disconnect the video board from the connector UW7 and
UW8 on the function board, and turn over the video board.
(4) From the reverse side of the video board, disconnect the
card wire from the connector VW3 on the video board, and
take out the video board.
Reference:
• Remove the tie band as required.
Fig.12
3.1.9 Removing the function board
(See Fig.13)
• Prior to performing the following procedures, remove the top
cover, fan motor, rear panel and video board.
(1) From the top side of the main body, disconnect the wires
from the connector PCN1 on the DVD mechanism
assembly.
(2) Disconnect the card wire from the connector UW4 and
UW6 on the function board.
(3) Remove the screw Nattaching the function board.
(4) Disconnect the function board from the connector CW5,
CW6 and CW7 on the main board.
Fig.13
K
Rear panel
M
L
H
Power cord
Video board VW3 VW4
ACW1
Tie band
UW7
UW8
Function board
Power cord
UW4UW6 DVD mechanism
assembly
CW5
CW6
CW7
N
Main boardFunction board
PCN1

1-10 (No.MB143)
3.1.10 Removing the main board
(See Fig.14)
• Prior to performing the following procedures, remove the top
cover, tray door, DVD mechanism assembly, fan motor, rear
panel, video board and function board.
(1) From the top side of the main body, remove the nine
screws Pattaching the main board.
(2) Disconnect the wires from the connectors ACW2, ACW3,
ACW4 and ACW5 on the main board and take out the main
board.
Reference:
• When attaching the screw P, attach the wire clamp together
with it.
• After connecting the wire to the connector ACW2, bundle the
wire using the wire clamp.
3.1.11 Removing the power trans
(See Fig.14)
• Prior to performing the following procedures, remove the top
cover, tray door, DVD mechanism assembly, fan motor, rear
panel, video board and function board.
(1) From the top side of the main body, disconnect the wires
from the connectors ACW2, ACW3, ACW4 and ACW5 on
the main board.
(2) Remove the four screws Qattaching the power trans.
Fig.14
Power trans
A
CW5
A
CW4
A
CW3
ACW2
P
Q
P
Q
P
Wire clamp

(No.MB143)1-11
3.2 Front panel assembly section
3.2.1 Removing the front board (See Fig.15)
• Prior to performing the following procedures, remove the top
cover, tray door and front panel assembly.
(1) From the back side of the front panel assembly, remove the
five screws Rattaching the FRONT board.
(2) Disconnect the wire from the connector UCW13 on the
front board.
(3) Take out the front board from the front panel assembly.
3.2.2 Removing the power SW board
(See Fig.15)
• Prior to performing the following procedures, remove the top
cover, tray door, front panel assembly and front board.
(1) Remove the screw Sattaching the power SW board.
(2) Take out the power SW board from the front panel
assembly.
Fig.15
Front board Power SW boardUCW13
R S
Wire

1-12 (No.MB143)
SECTION 4
ADJUSTMENT
This service manual does not describe ADJUSTMENT.

(No.MB143)1-13
SECTION 5
TROUBLESHOOTING
5.1 MAIN
5.1.1 POWER
Check for VCC(5V)
at FRONT PCB
;pin #17,46,72,90 of UIC1
Check for power-sense(5V)at FRONT PCB
;pin #77 of UIC1
When power on for FRONT PCB
Check for High Voltage(5V) at"M"com
;pin#74 of UIC1
Check low Voltage(0V)
at EXPAND IC (M66010)
;pin#32 of UIC500
Check for connector from DSP PCB to FRONT PCB
;VCW7
Check normal Voltage
at POWER PCB
AZD1 (5.1V, 1/2W)
Check pattern from VCW7
to pin#77 of UIC1
Replace Micom(UIC1)
If High Voltage (5V), check for Circuit protection
Check connector wire Ass'y of power
P/T - MAIN PCB(7P,ACW3)
MAIN PCB (8P,PW3)
Replace AZD1
Check resistant from GND
to pin #77 of MICOM(UIC1)
if the short(0 ohm),to replace
Micom(UIC1)
Check for Input voltage
at POWER PCB
;AIC1(7805)
Replace AIC1
Check for circuit at Sub Trans
;PBD2, PT1, AFS3(Fuse)
NO
NO
NO
NO
NO
YES
YES
YES
YES
YES
YES
NO

1-14 (No.MB143)
5.1.2 OUTPUT
YES
YES
YES
NO
NO
NO
NO
Check voltage at Main PCB
; VM, VL
Check Voltage for CW7
; 12V
Check Connector PW1
Check ABD2,4
Check Audio channel at CW5
for input:5.1 channel Audio signal
Check signal for FR/FL/C/W/RL/RR
at MAIN PCB
Check voltage for CW7(SPK Relay)
;High(5V)
Check Q4,Q5
Check circuit for AMP channel
;Out ports of FIC6, IC7, RIC5
Reference to NEXT page
; "A" position
Check circuit for Speak Relay

(No.MB143)1-15
5.1.3 Protection(When High Voltage at Protectiion port)
5.1.3.1 In this case "LOW" for, Base port of Q12(R2003 TR) at MAIN PCB
NO
NO
NO
NO
NO
YES
YES
YES
YES
YES
"A"
Check Voltage
for Main AMP of Main PCB
VM, VL
Check voltage for IC4
-12V Check circuit for voltage(-12V)
Check ABD 2,4
Check circuit for DC Voltage
Replace P/T, Q15
Check circuit for
Diode behind position
Check normal condition for Q15(C945)
;temperature-sense S/W be operated in the Power Trans
is Turn on
Check DC Voltage for Speaker port
Check the parts is normal?
;ZD6,ZD5(3.9V)
Check electric potention for PBD1, ABD1,PD3 at DVD Power PCB
;R33,R36(27K)
R34,R37 (150 Ohm)

1-16 (No.MB143)
5.1.3.2 In this case "LOW" for Base of Q13(A733) at Main PCB
5.1.3.3 Check the Connector Wire Ass'y Connectin of each PCB
Check the Turn on for channel of Q35(C945)
Check circuit for channel(Turn on)
according feedback "A"position of
previous page
;DVD MECHA - Main PCB (8P,PW3)
;POWER TRANS - Main PCB (ACW3)

(No.MB143)1-17
5.2 DVD Servo parts
5.2.1 Initial operation after power ON
(DVD Dual) (DVD single)
Y
Y
4
3
Y
N
N
N
Disc present or not
Disc present
POWER ON
CD or DVD judgement
DVD single or
Dual layer judgement
CD or CDRW
judgement
DVD single
initial setting
DVD Dual
initial setting
To Each disc playback
CD
initial setting
CDRW
initial setting
DVD
Single Dual
CD
CD CDRW
Is Tray closed? Tray close operation.
about 3sec.
Is Tray closed?
Stop Close operation.
Wait Open Command from MPEG
Laser Off
Monitor Display=NO DISC
Pick up headinitial position.

1-18 (No.MB143)
5.2.2 Play operation
Play
Disc Motor forced accelleration Repeat
seveal times
Change
Disc Type
Focus Seach
Track servo ON
CLV servo ON
Read TOC
Automatic Adjustment
Automatic Adjustment is done once
when the disc is replaced
Is focus servo
on?
Search Picture appears
6
7
8
5

(No.MB143)1-19
5.2.3 PickUp Head Initial Position
PickUp Head Initial Position
(1) 1. Move Pick Up Head to inner direction until pin5 of MJ4="L"
(2) 2. If pin5 of MJ4="L", then move Pick Up Head to outer direction for a short time.
(3) 3. Turn On the Laser of Pick Up Head to judge that disc is present or not.
Does Pick Up
Move to inner
direction?
Does Pick Up
Move to out
direction again?
Does Laser Turn
On?
Check voltage at
pin8 of RCN1 is
about 2.5V?
Check BUS line between RIC1 and
SIC1,SIC1 and MIC1
Is pulse of 2.5
+-2.5V developed
at pin3,4 of MJ4?
Is pulse of 2.5
+-2.5V developed
at pin13 of SIC1
Is pin5 of MJ4 =
"L" appeared?
Replace Pick Up Head
Check line between SIC1
and MJ4
Check
connection
between PCB
and MECHA
Check
connection
between PCB
and MECHA
Check
peripheral
circuit of SIC1
and DRIC1
Check BUS
line between
SIC1 and MIC1
N
N
N
N
N
N
N
Y
Y
Y
Y
Y
Y
3
OK

1-20 (No.MB143)
5.2.4 Disc Presence/Absense Judgment
Disc Presence Judgment
Turn On Laser
Does lens move
with UP/DOWN
full stroke in focus
direction?
Is focus search
voltage developed
at pin 11 of SIC1
Check PI
(pin36 of RU1)
signal and FE
(pin42 of RIC1)signal
Y
N
N
N
No Disc OK
Check connection between RIC1 and RCN1.
Check BUS line RIC1and SIC1.
Check RIC1
Check
peripheral
circuit of DRIC1
Check BUS
line between
SIC1 and MIC1
Y
YNo signal
Normal
Disc is presence
4