Sharp VT-3448X User manual

I
VT-3448X
VT-51 48X
’ SHARP
SERVICE MANUAL
S77Cl VT-3448X
TV/VCR COMBINATION
TELEVIDEO
9
VT-3448X VT-51 48X
,
MODELS
VT-51 48X
i
I
In the interests of user-safety (Required by safety regulations in some countries) the set should be restored to its
original condition and only parts identical to those specified should be used.
FEATURE
n Full Auto Search Tuning System
n On Screen Digital Channel/Sound Level/Tuning
Display, Control (Contrast, Colour, Brightness, Tint, P-
Tone) Symbol and Level
n Blue Back Off Timer
n 39 Key, Wireless Remote Control Unit
n Channel Skip
n High Speed and Double Speed Video Search System
l PAL : 3 times/7 times (SP/LP)
@ NTSC : 3 times/5 times (SP/LP)
5 times/l5 times (EP)
n DPSS (Digital Program Search System)
n Quick Start Playback with Full Loading System
n Digital Automatic Tracking Control
n Automatic Playback Function
n AHC (Automatic Head Cleaning System)
n Sharp Super Picture
CONTENTS
Page
l
SPECIFICATIONS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
l
IMPORTANT SERVICE NOTES . . . . . . . . . . . ..a............ 3
l
LOCATION OF USER’S CONTROL . . . . . . . . . . . . . . . . . . . . 4
l
DISASSEMBLY AND REASSEMBLY
. . . . . . . . . . . . . . . . . . 6
l ADJUSTMENT OF THE TV ELECTRICAL
CIRCUITRY
.................. ..~....................................
9
l
PRECAUTIONS IN REASSEMBLING . . . . . . . . . . . . . . . 23
l FUNCTION OF MAJOR MECHANICAL
PARTS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
l ADJUSTMENT, REPLACEMENTAND
Page
l TROUBLESHOOTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
l CHASSIS LAYOUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
65
l BLOCK DIAGRAM OF TV SECTION . . . . . . . . . . . . . . . . . 67
l DESCRIPTION OF TV SECTION
SCHEMATIC DIAGRAM
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
l BLOCK DIAGRAM OF VCR SECTION
. . . . . . . . . . . . . 85
l DESCRIPTION OF VCR SECTION
SCHEMATIC DIAGRAM
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
l PRINTED WIRING BOARD ASSEMBLIES...... 101
l
ASSEMBLY OF MECHANICAL UNITS . . . . . . . . . . . . . . 26
REPLACEMENT PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . 107
l PACKING
l ADJUSTMENT OF THE VCR
OF THE SET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
ELECTRICAL CIRCUITRY
. . . . . . . . . . . . . . . . . . . . . . . ..a...... 44
WARNING
The chassis in this receiver is partially hot. Use an isolation transformer between the line cord plug and power
receptacle, when servicing this chassis.
To prevent electric shock, do not remove cover.
No user -
serviceable parts inside. Refer servicing to qualified service personnel.
SHARP CORPORATION

VT-3448X
VT-51 48X
SPECIFICATIONS
E OF THE PRODUCT
Power Source:
Power Consumption:
Receiving Broadcast Standard:
Receiving Channel:
Receiving System:
Antenna Input Impedance:
Video Signal:
Audio Signal:
Temperature:
Dimensions (Approx.):
Weight (Approx.):
Cabinet Material:
Accessories:
220-240 VAC, 50 Hz
VT-3448X : 77 W
VT-5148X : 98 W
B/G
VHF; 1 A-S20
UHF; s21 -c57
Sound; 5.5 MHz
Colour; PAUNTSC (AV INPUT only)
VHF/UHF; 75 ohm Unbalanced (DIN)
Input;
0.5-2.0 Vp-p/75 ohm (RCA)
output; 1 .O Vp-p/75 ohm (RCA)
Input; 0.5 Vrms/lOk ohm (RCA)
output; 0.5 Vrms/l k ohm (RCA) (54% MOD)
Operation; 5°C to 40°C
Storage;
-1OOC to 60°C
VT-3448X : 352 mm (W) x 387 mm (H) x 382 mm (D)
VT-5148X : 504 mm (W) x 505 mm (H) x 470 mm (D)
VT-3448X : 12.4 kg
VT-5148X : 23.4 kg
Plastic
0 Operation Manual
0 Infrared Remote Control Unit
c] Dry Batteries, Type AA (x2pcs)
HTV SECTION
Viewing Area:
Picture Power:
Speaker Output:
Picture Tube:
WCR SECTION
VT-3448X : 33.54 cm Diagonal Measurement
VT-5148X : 50.8 cm Diagonal Measurement
VT-3448X : 22.0 kV at 800 uA Beam Current
VT-5148X : 25.0 kV at 1100 uA Beam Current
VT-3448X : 3.0 W at Max. (8 cm Round Dynamic xlpc)
VT-5148X : 3.0 W at Max. (8 cm Round Dynamic xlpc)
Type;
VT-3448X : VB370BVBKI S-S (Tint Tube)
VT-5148X : VB51 KPD12X/4E (Tint Tube)
Heater; VT-3448X : 6.3 V, 300 mA
VT-5148X : 6.3 V, 600 mA
Focus; High Bi-Potential Electrostatic
Outline:
Format:
Video Recording System:
Luminance:
Chrominance:
Video Signal System:
Cassette Tape:
Tape Width:
Tape Speed:
Recording/Playback Time:
VHS Video System Colour Video Cassette Recorder
VHS PAUNTSC Standard
Rotary Slant Azimuth 2-Head Helical Scan System
FM Recording
Low Frequency Converted Direct Recording
PAUNTSC 3.58MHz Colour
VHS Type Video Cassette Tape
12.7 mm
PAL ;
23.39 mm/s (SP), 11.70 mm/s (LP)
NTSC ;
33.35 mm/s (SP), 16.68 mm/s (LP.PB only), 11.12 mm/s (EP)
SP ; Max. 240 min (with E-240)
LP ;
Max. 480 min (with E-240, PAL only)
EP ; Max. 480
min (with T-160, NTSC only)
Note: The antenna must correspond to the new standard DIN 45325 (IEC 169-2) for combined UHF antenna with
75 ohm connector.
Specifications are subject to change without prior notice.
2

I
VT-3448X
VT-51 48X
IMPORTANT SERVICE NOTES
Maintenance and repair of this receiver should be done by qualified service
personnel only.
SERVICING OF HIGH VOLTAGE SYSTEM AND
PICTURE TUBE
When servicing the high voltage system, remove static charge from it by
connecting a IOk ohm Resistor in series with an insulated wire (such as a
test probe) between picture tube dag and 2nd anode lead. (AC line cord should
be disconnected from AC outlet.)
1. Picture tube in this receiver employs integral implosion protection.
2. Replace with tube of the same type number for continued safety.
3. Do not lift picture tube by the neck.
4. Handle the picture tube only when wearing shatterproof goggles and after discharging
the high voltage completely.
X-RAY
This receiver is designed so that any X-Ray radiation is kept to an absolute
minimum. Since certain malfunctions or servicing may produce potentially
hazardous radiation with prolonged exposure at close range, the following
precautions should be observed:
1. VT-3448X:
When repairing the circuit, be sure not to increase the high voltage to more
than 25.3 kV, (at beam 0 PA) for the set.
VT-51 48X:
When repairing the circuit, be sure not to increase the high voltage to more
than 29.3 kV, (at beam 0 PA) for the set.
2. VT-3448X:
To keep the set in a normal operation, be sure to make it function on 22.0 kV
+ 1.5 kV - 2.0 kV (at beam 800 PA) in the case of the set. The set has been
factory - Adjusted to the above-mentioned high voltage.
VT-5148X: To keep the set in a normal operation, be sure to make it function on 25.0 kV 2
1.5 kV (at beam 1100 PA) in the case of the set. The set has been factory -
Adjusted to the above-mentioned high voltage.
* If there is a possibility that the high voltage fluctuates as a result of the repairs, never . .
forget to check for such high voltage after the work.
3. Do not substitute a picture tube with unauthorized types and/or brands which may cause
excess X-ray radiation.
BEFORE RETURNING THE RECEIVER
Before returning the receiver to the user, perform the following safety checks.
1. Inspect all lead dress to make certain that leads are not pinched or that hardware is not
lodged between the chassis and other metal parts in the receiver.
2. Inspect all protective devices such as non-metallic control knobs, insulating fishpapers,
cabinet backs, adjustment and compartment covers or shields, isolation resistor-capac-
ity networks, mechanical insulators etc.
3

VT-3448X
VT-51 48X
LOCATION OF USER’S CONTROL
STOP/EJECT button
POWER button
EO/AUDIO INPUT terminals
01 VA A VCH A S.PICTlJRE.REC
CHILD-LOCK indicator
PROGRAM TIMER Indicator
REC indicator
POWER/WAKE-UP TIMER
indicator
button SHARP SUPER PICTURE button
(This function WIII create a clearer image dunng playback.)
CHANNEL UP/DOWN buttons
VOLUME UP/DOWN buttons
I Rear1
VIDE IO
INPUT
--.I
I
? AUDIO
VIDEO
OUTPUT
ANTENNA IN terminal
INPUT
OUTPUT
This operation manual is for VT-3448X and VT-
4

LOCATION OF USER’S CONTROL (Continued)
I Remote Control I
TVA/IDE0 Select button
STANDBY/ON button
CHANNEL SELECT buttons-,
FLASHBACK button
Returns to previously
viewed channel.
COUNTER RESET button
l Used to reset the tape
counter.
TAPE SPEED button
l Used to select the recording
tape speed.
------\Y
PLAY button
l Used for tape playback.
l Used to cancel the PAUSE/
STILL mode and return to nor-
mal playback operation.
/--
REW button 2
l Used to rewind the tape or to
conduct Reverse Video Search
during playback mode.
REC button
l Used to record a programme.
CONFIRM button -
l Used to confirm the
programme setting.
Infrared Transmitter Window
DISPLAY button
l Used to change the On
Screen Dtsplay
I-MI ITF hl attnn
sound Press + Mutes
Press again + Restores
sound to previous level.
VOLUME UP/DOWN buttons
CHANNEL UP/DOWN
buttons (TRACKING ,@/@)
l Used to select the
CHANNEL.
l Used to adjust the TRACK-
ING whrle playing the tape
CHILD-PROOF LOCK button
l Used to lock any selected
mode.
FF button
l Used to fast forward the
tape or to conduct Forward
Video Search dunng play-
back mode.
STOP button
l Used to stop the tape.
PAUSE button
l Used to temporarily stop the
tape during recording mode.
l Used to display a still
picture during p!ayback
mode.
SHARP
DPSS buttons
TV-VCR COMBINATION
l Press the (s/e) button to
search for the Index signal
and begin playback auto-
matically.
RETURN button -----/
SET button /
PROGRAMME button
. Press the button to set the
programme Timer.
n Installing dry batteries in the remote control unit
I,.....- MENU button
l Used to select the menu
screen.
Before using the TV set for the first time, install the supplied dry batteries in the remote control.
Inserting batteries
0 With your thumb nail, pull up the slit as indicated by the arrow
to remove the back cover.
Pull up
@Insert two batteries (size “AA”). Be sure to match the battery
O/O terminals with the @/@ marks inside the compartment.
@Replace the battery cover.
l Remove batteries if weak or if the unit IS not in use for long periods.
l Do not mrx old and new batteries.
l Incorrect installation of the batteries may damage the remote control.
5

VT-3448X
I
VT-51 48X 1
DISASSEMBLY AND REASSEMBLY
1. Remove the 9 rear cover fixing screws and detach the rear cover.
2. Take out the anode cap, CRT PWB, connectors F and G, coating ground, SP chip, fixing screws and others.
3. Remove the 2 Main PWB fixing screws and take out the Main PWB unit and the Power PWB unit.
4. Remove the 4 Power PWB fixing screws, and take out the Power PWB unit.
VT-3448X
c--l
1
VT-51 48X

DISASSEMBLY AND REASSEMBLY (Continued)
4
5. Remove the 7VCR fixing screws, and detach the shielding case.
6. Remove the 4 cassette housing control fixing screws, and detach the cassette housing control.
7. Remove the 2 Power SW PWB fixing screws, and detach the Power SW PWB.
8. Remove the 6 mechanism chassis fixing screws, and detach the mechanism chassis from the Main PWB.
9. Remove the 4 Main PWB fixing screws, and detach the Main PWB.
0
6

DISASSEMBLY AND REASSEMBLY (Continued)
For servicing any of the components inside, disconnect the lead dressing holder. Position the main PWB unit upright
as shown below and connect the leads for starting the services.
Note: Fit the VCR unit the front cabinet with the front flap door tilted at 70-80”.

I
VT-3448X
VT-51 48X
ADJUSTMENT OF THE TV ELECTRICAL CIRCUITRY
ADJUSTMENT PRECAUTIONS
1. Calling the service mode
(1)
Place the set in the stand-by mode.
(2)
Hold down the CH UP button (CH A) of the set for 3 seconds or longer. Then press the STAND BY/ON button
(&I) of the set.
(3) Now the set will be in the service mode.
2. Getting out of the service mode
There are three ways to get out of the service mode.
(1)
Press the MENU key on the remote controller.
(2)
Bring the set into the stand-by mode.
(3) Turn off the MAIN POWER switch.
3. On-screen display in the service mode
A service mode item and its data appear in two lines
at the lower left on the screen. Top line : Service mode item (See below)
\
Bottom line : Data (See below) bW
Service mode
Item Display
Data Variable range
DIRECT MODE DIRCT * Adjustable in the DIRECT MODE
V-AMPLITUDE V-AMP 0 - 127 R CUT OFF
(0 - 255)
V-LINEARITY V-LIN 0 - 31 G CUT OFF
(0 - 255)
V-OUT PHASE v-POS o- 7 B CUT OFF (0 - 255)
H-POSITION H-POS
0 - 31
G DRIVE GAIN (0 - 255)
BELL FILTER BELL
o- 3B DRIVE GAIN
(0 - 255)
R-Y BLACK OFFSET
R-Y
o- 15
B-Y BLACK OFFSET B-Y o- 15
Y-SUB CONTRAST
CONT 0 - 31
SUB COLOUR
COLOR
0 -240
SUB BRIGHT BRI
0 -150
SUB TINT TINT 0
- 37
Note :
Item selectable by the CH Av keys and data by the VOL Irv keys (effective on both the
remote controller and the set)
The numeric keys on the remote controller work as follows in the DIRECT mode only.
R CUT OFF
G CUT OFF
B CUT OFF
G DRIVE GAIN
B DRIVE GAIN
UP
DOWN
1 4
2
5
3
6
7
5
8 0
Notes :
In all the other modes, these keys are used to select channels.
In the DIRECT TUNING mode, these keys are used to enter data.
9

VT-3448X
VT-51 48X I
Item-by-item control in the service mode
1. DIRECT mode
F-B/W
o->I (forced B/W)
2. DIRECT mode + HOR. POS. mode
DRV CNT 0->I (drive forced center)
SUB-BRIGHT Initial value
R.G.B. CUTOFF 0
(E2PROM data resumed when any of the “1” thru
“6” keys on the remote controller is pressed)
3. R-Y Black Offset
4. B-Y Black Offset
CONTRAST MAX (USER-CONTROL)
BRIGHT MAX (USER-CONTROL)
COLOUR CENTER (USER-CONTROL)
R-MONITOR SW 0 - > 1 (MONITOR OUT)
MUTE MODE
Y-MUTE
CONTRAST MAX (USER-CONTROL)
BRIGHT MAX (USER-CONTROL)
COLOUR CENTER (USER-CONTROL)
B-MONITOR SW 0 - > 1 (MONITOR OUT)
MUTE MODE Y-MUTE
5. SUB Tint MUTE MODE
Y-MUTE
6. Unspecified items PICTURE NORMAL (CONT. BRI. COL.)
Note :
All the settings will be back to the initial ones when shifting into any other mode or getting out of the
service mode.
Allocation of special keys in the service mode
*HORIZONTAL POSITION key CONFIRM (SET
-> S-PICTURE)
*Y-MUTE KEY SET
*COLOUR MAXIMIN. select key TIMER ON/OFF
*DIRECT TUNING MODE KEY
RETURN
*VCR SLOW TEST KEY
PROG
*NVM MODE KEY DISPLAY
Adjustment precautions
1) Basically follow the sequential order of adjustments.
(Unless otherwise specified, follow the adjustment procedures.)
2) The “*“-marked steps in the adjustment procedures are automatically taken when in the service mode. Leave
out these steps.
3) For adjustments in the service mode, it is necessary to have the remote controller at hand.
Trouble indicators
If the set is interrupted by the protectors, the following indicators work to identify a spot in trouble.
’
1) &I LED (red) flashing : Deflection system protector activated
2) REC LED flashing (high-voltage or beam protector)
: IIC bus line error
3) LED off
(VCJ or tuner, EEPROM)
: Power protector activated
(+B line short-circuited)