Xoceco TK2450 Schematic

COLOR TELEVISION

TK2450

CONTENTS

Safety instruction………………………………………………………………………1
General instruction……………………………… ……………………………………… .1
Alignment instruction……………………………………………………………………2
Alignment flow ..……………………………………………………………………..2
Alignment method…………………………………………………………………..3
BLOCK DIAGRAM………………………………………………………………………... 8
MAIN IC……………………………………………………………………………….. 9

Parts list………………………………………………………………................13

Exploded view …………………….………………………………………………31
Schematic diagram…………………………………………………………………. 33

Note: This service manual is only for professional service personnel’s reference. Before

servicing the unit, please read the following items carefully.

1 safety instruction

1.1 X-RAY radiation precaution

1.1.1 Excessive voltage will cause harmful X-ray. To avoid this radiation hazard, the high voltage should
fall within the limitation. The appliance works at AC 120V, 60Hz. The high voltage of zero beam current
should be within 29.0kV on condition that the main power (B+) voltage is AC135V. And it should not
exceed 30kV in any condition.
* Keep the main power voltage at 135V when checking the high voltage.

1.1.2 The primary source of X-RAY RADIATION is the CRT. The CRT of this TV set have gotten the
approval of safety authenticat ion i nspect ion. The rep lacem ent CR T should be exactly the same type and
specification CRT which has gotten a similar safety approval, and check the high voltage according to
the HIGH VOLTAGE CHECK procedure.

1.2 safety precaution
a. Since the power supply circuit of this receiver is directly connected to the AC power line, an isolation
transformer is necessary during dynamic service to avoid possible shock hazard.
b. Always discharge the graphite layer conductor when moving the CRT.
c. Disconnect the power cord before replacing parts.
d. When replacing high-power resistor, keep the resistor 10 mm away from the circuit board.

1.3 Component safety precaution
Many electrical and mechanical parts in the chassis have special safety-related characteristics. These
characteristics are often passed unnoticed by a visual inspection. Replacement parts which have these
special safety characteristics are identified in this manual and its supplement electrical components
having such features are shaded or marked by on the schematic diagram and the parts list. Before
replacing any of these components, read the parts list in this m anual carefully. The use of substitute
replacement parts which do not have the same characteristic as specified in the parts list may create
shock, fire, X-RAY RADIA TI O N or other hazards.

2.General instruction

2.1 Copy the standard model dat a t o let EEPROM of the chassis have those d ata bef ore placing it on the
unit, do “factory adjustment” if necessary. If use a blank EEPROM directly, you should preset IIC data
and then do other common adjustment. Refer to TABLE1 to preset EEPROM.

2.2 the adjustment should be done under following circumstances without additional instruction
a) Alternating current 120V/60Hz
b) Preheat at least 30 min

2.3The unit has auto degaussi ng circuit , the auto de gaussing proce ss can be finishe d within 1s w hen the
main power. only when turn on the unit at least 30min after last time turn off TV does the auto
degaussing circuit work.

2.4 If the CRT with magnetism affects color purity and convergence, when t he aut o degaussing
eraser . if the color purity and convergence are st ill not very good, then corresponding adjustment
should be done. Refer to picture tube adjustment method for adjustment.

Alignment instruction

3

1

3.1 Debugging item

N

a)adjust mode instruction
b)B+ voltage adjustment
c)RFAG C voltage adjustment
d)focus adjustment
e)Screen-grid voltage white balance, sub brightness adjust ment
f)filed scan center , line , amplitude adjustment
g)H-scan center adjustment

3.2 Alignment flow

+B adjustment

ormal

temperature aging

Focus adjustment

AGC adjustment

White balance
adjustment

Picture adjustment

Fig-1 alignment flow

3.3 Enter/exit factory adjustment method
Use remote control, press “MENU” button, then press 6483,”M”will appear on screen to show that you
have entered the factory adjustment method, press “STANDBY” to exit it.

3.4 Select adjustment item and adjust data
After entering factory adjustme nt mode, press 1-4 n umber button s to select menu1- menu4; To enter into
MENU0~MENU5, press “CHILD LOCK” button and then the number button (5~0) to enter into relative
menus. Press “P+” and “P-” to select and “V+” and “V-”to adjust.

4 Alignment method

4.1 B+ voltage adjustment
a) connect B+ point with a digital voltmeter to measure the negative pole of VD524
b) receive PHILIPS test pattern signal and set the picture to standard.
c) Adjust VR501 to let the value of B+ voltage be 135 V ±0.5 V (yongxin super pure flat)

4.2 AGC adjustment

a) receive VHF-H band,60 dB RF signal.
b) Select factory menu2 of “AGC”.
c) Press “V+”,”V-”to let voltage value of tuner pin AGC be 3.8 V ± 0.1 V(DC).(if the selected tuner

is changed, then the voltage of AGC should be measured again: receive VHF-H band and 60
dB RF signal, adjust AGC-TOP to let the picture just without noisy, then the voltage of tuner
AGC is the required value for adjustment.)

d) exit factory menu

4.3 Normal temperature aging

a) do not receive signals.

2

b) under ”M” condition, set the accelerator to an appropriate point for aging.

4.4 Accelerator adjustment

a) do not receive signals;
b) select “SC” of factory menu3 to let the field scanning stop working.
c) adjust acceleration potentiometer to let bright lines just appears on screen.
d) exit SC menu.

4.5 High voltage check

Note: the main power voltage (B+=135 V)can affect the high voltage directly, so be sure to let the B+
power voltage accurate. Under any state, the high voltage should not exceed 30 kV.

a) connect an accurate high voltage meter between the second anode cap of picture tube and

ground.

b) turn on TV and receive testing card signal.
c) set picture to standard, the high voltage should be 27 kV± 1 kV.
d) the high voltage should not exceed 30KV with minimum brightness and contrast.

4.6 Focus adjustment

a) receive PHILIPS signal
b) adjust focus electrode potentiometer on FBT to optimize B area focus of screen.

4.7 White balance adjustment (color temperature 12000°K± 8MPCD,X=0.270± 0.008,Y=0.283± 0.008)

a) receive full white signal
b) select factory menu3
c) on the basis of blue, adjustment RD,GD of M3, let to white balance coincide with standard.

4.8 Filed scanning adjustment (fig-2)

a) receive PAL of PHILIPS test pattern signal.
b) select factory menu1
c) adjust V- SLO PE menu to let the horizontal center line of test pattern above blanking.
d) select V- SHI FT menu and adjust to let the vertical center of picture coincide with

vertical center of picture tube.
e) Select V-SIZE menu and adjust to let the vert ical reproduct ion ratio of picture acceptable.
f) Adjust V.SC to optimise the vertical S correction of picture.
g) Receive NTSC PHILIPS test pattern and readjust the above items.

4.9 Horizontal scanning adjustment (Fig-3)
a) Receive PAL PHILIPS signal
b) Select factory menu1
c) Select H.SHIFT menu and adjust to let the scanning horizontal center coincide with mechanical

center of picture tube
d) Exit M3 menu
e) Adjust VR433 to let horizontal reproduction ration of picture acceptable
f) Adjust VR432 to minimize left-right edge pincushion distortion of picture

Horizontal line

Under part banking

Fig-2 field scan adjustment

3

g) Adjust VR431 to minimize trapezoidal distortion
h) Exit factory menu

a

4.10 Sub-brightness adjustment
a) Receive PAL-D/K PHILIPS signal
b) Select “SB” of factory menu3
c) Adjust “SB” to let things between the sixth and seventh grey scale clear

4.11 OSD adjustment
a) Receive PAL-D/K PHILIPS signal
b) Select OSD H and OSD V of factory menu4. Adjust OSD H and OSD V to let OSD at a specified

place.
c) Exit factory menu

4.12 Degaussing
a) The unit has and auto degauss ing circuit, the degaussing circuit works several seconds after turning

on TV
b) If you want to move TV or change the direction, turn off TV and ten minutes later the degaussing

circuit will work
c) For better degaussing effect, you can use magnetic eraser
d) Move the magnetic eraser clockwise before your TV, when it is 2m away from your TV, turn off the

magnetic eraser. If the effect is still not very good, you can adjust “color pur it y” and “convergence”

4.13 Color purity correction
a) Turn on your TV
b) At least 15 minutes later, use anti-magnetized coil for degaussing
c) Obtain maximum brightness and contrast
d) Select factory menu3 and adjust to let R and B be zero, then let only green raster appear on the

screen at the moment
e) Loosen screws of deflection yoke frame to let vertical green belt appear on screen only
f) Move the rubber wedge
g) Rotate along neck of picture tube and slide color-purity magnets until the green belt at the middle of

screen and is vertical at the same time
h) Slowly move the deflectio n y oke backw ard of forwar d until the w h ole gre en rast er appears on scree n,

tighten the screws of the deflection yoke
i) Check the color purity of red raster and blue raster
j) Adjust white balance again to obtain white raster

4.14 Convergence correction

4.14.1 Central convergence correction
a) Turn on your TV

Fig-3 line scan adjustment

4

b) At least 15 minutes later, receive square test pattern signal
c) Adjust brightness and contrast to get the best picture
d) Adjust the angle of two tetrode magnetic rings to let the red vertical line coincide with the blue

vertical line at middle of screen
e) Keep the angle unchanged, move the two tetrode magnetic rings at the same time to let t he red and

blue horizontal lines coincide at middle of screen
f) Adjust two hexode magnetic rings to let the green line coincide with the mixed line of red and blue.

Adjust the angle between them will affect the vertical line, move them together will affect the

horizontal line.
g) Repeat d), e), f) and observe the movement of red, green and blue.

4.14.2 Ambient convergence correction
a) Turn on your TV
b) At least 15 minutes later, loosen the screws of the deflection yoke
c) Fixate the rubber wedge temporarily under the deflection yoke
d) Move the deflection yoke upward or downward to get best convergence, push the rubber wedge into

space between picture tube and deflection yoke to fixate the deflection yoke temporarily
e) Place the rubber wedge whose overlay paper has been removed at t he bot tom space
f) Move the deflection yoke left and right to get best convergence
g) Keep the condition unchanged, place another rubber wedge whose overlay paper has been

removed also at the upper space at the same time
h) Remove the interim rubber wedge, adhere it to picture tube and deflection yoke
i) After placing three rubber wedges, check all the convergence again
j) Stick three transparent viscous belts to the rubber w edge

2

Chart 1 I

2

C standard UOC for export bus control adjustment i tem default setting

I

C TDA (NOM)8377-B-6NA E2PROM pre-set data

MI Items Variable Preset

M0 SUBCON 56(sub-contrast)

SUBCOL 56(sub-chroma)
SUBSHP 48(sub-acutance)
SUBTINT 31(sub-hue)

M1 V.SLOPE 34(field center adjustment)

V.SHIFT 27(field point adjustment)
V.SIZE 36(field amplitude adjustment)
V.SC 32(field line )
HSHIFT 32(line point adjustment)
PROGRAMA.NO 2(channel)

M2 AGCTAKEOVER 24(AGC adjustment)

SHIPPING 0(leav e fact ory set)

M3 BT 75(adjust white balance of brightness)

5

CT 75(adjust white balance of brightness contrast)
SC OFF
RB 32(red cut off level adjustment)
GB 32(green cut off level adjustment)
RD 32(red cut off level adjustment)
GD 32(green cut off level adjustment)
BD 32(blue cut off level adjustment)
SB 40(sub brightness adjustment)

M4 OSD.V.POSITION 10(OSD position)

OSD.H.POSITION 5(OSD H-position)
BTSC-MODE MONO(STEORO,SAP )
BTSC-ST 13
BTSC-SP 12
BTSC-L1 1
BTSC-A1 15
BTSC-A2 0
BTSC-TC 0
BTSC-STS
BTSC-ADJ

MI Items Variable Preset

M5 MODE STANADARD(standard, soft, floweriness)

BRIGHT 75

COLOR 50
SCBRIGHT 20
YDELAYTV 12
YDELAYAV 12

M6 OSO 1(field over-scan switch)

AGCSPEED 1(AGC of speed)
FFI 0(IF PLL SPEED)
FMWS 1(frequency range of sound OFF=225KHZ,ON=450KHZ)
RP0 0(pre-shock and over-shock scale)
NTSCMATRIX USA
VOLPIN 0(1:push-pull output; 0: OC gate output.)
SOFT CLIP 3(white level limit)
PEAK WHITE 15(peak white limit)
CORING 0(coring noise reduction)

M7 AV2 1

SVHS 1
YUV 1

CONTRAST

0

75

6

VOLADJPOING 1(volume value have:1,25,50,75)
VOLVALUE 20(volume curve value:20,60,75,90)

M8 CATHOOELEVEL 7(cathode level)

UOCVOLUME 0(0:PWM terminal control; 1:UOC sound amplitude control of

inside)
FMATT 45(UOC sound output of amplitude) BTSC : 38
COMBFILTRE 0(N comb filter)
HEADPHONE 0(earphone function selection)
VM OPTION 0(VM function selection)
FRANCE 1 French
SPANISH 1 Spaish
POTUGUES 1 Portuguese

M9 NOM8377-B-6NA

STARTON 2(turn on)
STARTTIME 8(turn on time)
IF OFFSET 32(IF compensate)
TUNER OPTION 0(BXATB01 1F---X/ BXATB108F---K) 1 (BXATB017F---K) 2(XXX)

7

Block diagram

rCb

L

DY

S

F

S

TUNER

POWER

UNIT

SAW

135V

24V
16V

8V
5V

3.3V

S

TRAP

24C08

video

bus

TDA8377

IF IN Y IN

RF AGC V IN

U IN
CVBSINT
CHROMA
IFVO OUT
CVBS/Y IN

SDA
SCL

AUDIO OUT IK
RGB OUT
V OUT H OUT

V IN

TDA8177

V OUT

H IN

H OUT

H OUT

video

200V
+15V

-15V

Y

C

CRT PCB

CREEN

OCU

audio

video

CRT

video

4052

audio

N801

video

audio

Y

C

BU4052

V1i

ARo

ALo

ARi2
ARi1

A

ALi1

AN7522

Vi1

OUT1-

OUT1+

Vi2

OUT2-

OUT2+

Vo
V2i

S-VHS

i2

8

MAIN IC 8377:

ICs functional description

UOC TDA8377

SYMBOL PIN DESCRIPTION

STAND BY output. 1 In STAND BY mode, high level (Power OFF).

For Power ON this pin will be reduced to low.
SCL 2 I2C-bus clock line
SDA 3 I2C-bus data line
TUNING 4 tuning V o ltage (Vt) PWM output
P3.0/NTSC SW 5 Port 3.0 or NTSC output/SCART SW input, Forced NTSC selection,

Low-level output, otherwise High output.
KEY 6 Control keys input *3

9