Xoceco TJ-2768 Schematic

COLOR TELEVISION

TJ# series

TJ2768 TJ2778

TJ306

America

CONTENTS

Safety precautions………………………………………………………………………..… Alignment instructions. ………………………………….………..…………………….… Working principle analysis of the unit……………………………….………….…………. Block diagram………………………………….. ……………………………………….………… IC block diagram………………………………………………………………………..…… Wiring diagram ……………………………………………………………..……………... Troubleshooting……………………………………………………………………………..…… Schematic diagram. ………………………………………………………………………..

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Attention: This service manual is only for service personnel to take reference with. Before

servicing please read the following points caref ully.

Safety precautions

After the original service problem has been cor rected, a check should be made of the f ollowing:

FIRE & SHOCK HAZARD

1. Be sure that all components are positioned in such a way as to avoid possibility of adjacent component shorts. This is especially important on those chassis, which are transported to and from the repair shop.

2. Never release a repair unless all protective devices such as insulators, barriers, covers, shields, strain reliefs, and other hardware have been reinstalled per original design.

3. Soldering must be inspected to discover possible cold solder joints, frayed leads, damaged insulation (including A.C. cord), solder splashes or sharp solder points. Be certain to remove all loose foreign particles.

4. Check for physical evidence of damage or deterioration to parts and components, and replace if necessary follow original layout, lead length and dress.

5. No leads or components should touch a receiving tube or a resistor rated at 1 watt or more. Lead tension around protruding metal surfaces must be avoided.

6. All critical components such as fuses, flameproof resistors, capacitors, etc. must be replaced with exact factory types. Do not use replacement components other than those specified or make unrecompensed circuit modifications.

7. After re-assembly of the set always perform an A.C. leakage test on all exposed metallic parts of the cabinet, (the channel selector knob, antenna terminals, handle and screws) to be sure the set is safe to operate without danger of electrical shock. Do not use a line isolation transformer during this test. Use an A.C. voltmeter, having 5000 ohms per volt or more sensitivity, in the following manner: connect a 1500ohm 10watt resistor, paralleled by a 0.15uF. 150V A.C. type capacitor between a known good earth ground 9water pipe, conduit, etc. and the exposed metallic parts, one at a time. Measure the A.C. voltage across the combination of 1500ohm resistor and 0.15uF capacitor. Reverse the A.C. plug and repeat A.C. voltage measurements for each exposed metallic part. Voltage measured must not exceed 0.75 volts R.M.S. This corresponds to 0.5 milliamp A.C. Any value exceeding this limit constitutes a potential shock hazard and must be corrected immediately.

GRAPHIC SYMBOLS:

It is intended to alert the service personnel to the presence of uninsulated dangerous voltage that may be of sufficiently magnitude to constitute a risk of electric shock.

It is intended to alert the service personnel to the presence of important safety information in service literatur e.

X-RADIATION

Too 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 35KV on condition that the main power(B+) voltage is DC140V . And it should not exceed 36KV in any condition.

1. Be sure procedures and instructions to all service personnel cover the su bject of X-rays in current TV is the picture tube. However, this tube does not emit X-rays when the high voltage is at the factory specified level. The proper value is given in the applicable schematic. Operation at higher voltages may cause a failure of the picture tube or high voltage supply and, under certain circumstances, may produce radiation in excess of desirable levels.

2. Only factory specified C.R.T. anode connectors must be used. Degaussing shields also serve as X-ray shield in color sets. Always re-install them.

3. It is essential that the serviceman has available an accurate and reliable high voltage meter. The calibration of the meter should be checked periodically against a reference standard. Such as the one available at your distributor.

4. When the high voltage circuitry is operating properly there is no possibility of an X-radiation problem. Every time a color chassis is serviced, the brightness should be run up and down while monitoring the high voltage with a meter to be certain that the high voltage does not exceed the specified value and that it is regulating correctly. We suggest that you and your service or ganization review test procedures so that voltage regulation is always checked as a standard servicing procedure. And that the high voltage r eading be recorded on each customer s invoice.

5. When troubleshooting and making test measurements in a receiver with a problem of excessive high voltage, avoid being unnecessarily close to the picture tube and the h i gh v oltage compartment. Do not operate the chassis longer than is necessary to locate t he cause of excessive voltage.

6. Refer to HV, B+ and Shutdown adjustment procedures described in the appropriate schematic and diagrams. Too excessive voltage will cause harmful X- r ay.

IMPLOSION

1. All direct viewed picture tubes are equipped with an integral implosion protection system, but care should be taken to avoid damage during installation. Avoid scratching the tube. If scratched, replace it.

2. Use only recommended factory replacement tubes.

TIPS ON PROPER INSTALLATION

1. Never install any receiver in closed-in recess, cubbyhole or closely fitting shelf space over, or close to heat duct, or in the path of heated airflow.

2. Avoid conditions of high humidity such as: Outdoor patio installations where dew is a factor. Near steam radiators where steam leakage is a factor, etc.

3. Avoid placement where draperies may obstruct rear venting. The customer should also avoid the use of decorative scarves or other coverings which might obstruct ventilat ion.

4. Wall and shelf mounted installations using a commercial mounting kit, must follow the factory approved mounting instructions. A receiver mounted to a shelf or platform must retain its original feet(or the equivalent thickness in spacers) to provide adequate are flow across the bottom, blots or screws used for fasteners must not touch and parts or wiring. Perform leakage test on customized installations.

5. Caution customers against the mounting of a receiver on sloping shelf or a tilted position, unless the receiver is properly secured.

6. A receiver on a roll-about cart should be stable on its mounting to the cart. Caution the customer on the hazards of trying to roll a cart with small caster s acr oss t hresholds or deep pile carpets.

Alignment instructions

1. General instructions

1.1 The program data should be copied into the EEPROM (N802 M24C16) in this set according to Standard Sample program data, then execute “Factory Adjustment”. If adopt empty EEPROM, please preset I2C datum before any debugging.

1.2 If ther e is no special not ice, the unit adjustment should be done on the following conditions: a. AC power 120V/60Hz. b. Pre-heat the set for above 30 minutes.

1.3 There is a auto-degaussing circuit inside which could degauss the set automatically within one second after turn on the power. The auto-degaussing circuit effects on condition that every interval of turning on the set is longer than 30 minutes at least.

1.4 The magnetized CRT will influence the colour purity and focus. When the inside degaussing circuit can’t degauss thoroughly then an outside degausser is necessary. Colour purity and focus adjustment should be executed according to the colour purity and focus adjusts procedures if the colour purity and focus is not good.

2. Alignment items and procedure

a) B+ voltage check b) OSD character center adjustment c) AFT and RFAGC voltage adjustment d) Focus adjustment e) Screen-grid voltage adjustment f) White balance adj ust ment g) Horizontal and vertical scanning centre and amplitude adjustment h) Raster correction adjustment i) HDTV white balance adjustment j) HDTV Horizontal and vertical scanning centre and amplitude adjustment k) HDT V raster correction adjustment

Adjustment flow-chat is shown as Fig-1

E2PROM copy

High voltage check

B+ voltage

OSD position

AFT adjustment

AGC adjustment

Focus

Screen-grid voltage and w hite

balance adjustment

Centre of scanning amplitude and

raster adjustment

X-ray protection check

Filament voltage

SELF CHECK

Picture parts

Sub-brightness

White balance

Colour purity and convergence

Stereo check

Video/S-VHS/DVD

Check

Auto adjustment

The unit and remote Control function

Fig-1 Adjustment flow-chart

3. Factory mode adjustment

3.1 Enter factory mode adjustm ent Press the “factory menu” butt on on t he r emote control, the screen display the factory menu.

3.2 factory menu operation method Press the channel +/- button to selection the sub menu of factory menu, and press the vol+/- to enter the sub menu or setting the value.

3.3 exit the factory menu Press the MENU button again and again; it can exit the factory menu.

4. Adjustment methods

4.1 B+ voltage adjustment a. Be sure the voltage AC 120V/60Hz. b. Connect the digital voltmeter to TP3 and GND of B+ test point, input the US-7 signal, set the

picture control to “standard”, adjust RP501 to let the B+(test point) voltage 140V+/ - 0.3V

c. In the STAND BY t urn off, B+ voltage about 20V

4.2 OSD position adjustment In the factory menu, select SYS SETTING sub menu, adjust OSD H-POS item, let the character position to screen display center.

4.3 AFT adjustment a. IF of tuner (TUNER101) output and TP6 are separate. b. Input 45.75MHz of frequency and 90db of amplitude signals to TP6 c. Adjust the tunable inductance L110, and measure between the TP4 and GND voltage, until the

TP4 voltage to be 2.5V.

d. Output pin IF of TUNER101 and TP6 bonding pad is normal.

4.4 AGC voltage adjustment a. Receive 60db split field signal b. Adjust the potentiometer RP101, and measure the TP5 to GND voltage, until the voltage of TP5

to be 3.5V, t hen noise wave of t he pict ur e point disappears.

4.5 focus adjustment a. Receive A28 signal, set the picture mode to standar d. b. Adjust focus potentiometer of FBT, until the B area display best.

4.6 Screen-grid voltage and white balance adjustment a. Receive US-7 split field signal, the picture mode to “warm”. b. In the factory menu, select the W HITE BALANCE SETTING menu, fixed the CUT OFF R and

adjust the CUT OFF G and the CUT OFF B, until the white balance is norm al.

c. Select t he color and contrast to 0, select the brightness to 50 in the user menu. In the factory

menu, select the LUMINANCE SETTING menu; adjust the Brightness min, until the back level voltage about 180V. Adjust the SCREEN potentiometer, until rightmost of gray of the US-7 picture up and down separate.

d. Select the color to 0, the brightness to 50 and the contrast to 100 in the user menu, adjust the

Contrast max, until the eight level g r ay amplitude Vp-p to 100V.

e. Select the color to 0, the brightness and the contrast to 100 in the user menu, adjust the

BRIGHTNESS max, until low right back color of the D-8 picture does not white.

f. In the factory menu, select the WHITE BALANCE SETTING sub menu; adjust the white balance

(color temperature to 12000K+/- 8MPCD, the color coor dinat e to 0.270+/-0.008, 0.283+/-0.008).

4.7 Horizontal and vertical scanning centre adjustment of TV

4.7.1 Horizontal center adjustment Receive A6 signal, the picture mode to “STANDARD” in the factor y menu, select Horizontal

setting menu, adjust the H PO S, until the picture H-center and screen center accord.

4.7.2 Vertical center adjustment Receive A6 signal, the picture mode to “STANDARD” in the factory menu, select Vertical

setting menu, adjust the V PO S, until the picture V-center and screen center accord.

4.8 Vertical scanning adjustment Receive A12 signal, the picture mode to “STANDARD” in the factory menu, select Vertical setting

menu, adjust the V SIZE, until up and down over scanning of the picture to 8% of the all screen.

4.9 Raster correction and horizontal amplitude adjust ment of TV Receive white grid of NTSC signal, the picture mode to “STANDARD” in the factory menu, select horizontal setting menu, adjust the PCC, until the raster distort least, adjust the H SIZE, until r ight and left over scanning of the picture t o 8% of the all screen.

4.10 If the scanning line distortion and raster geometric distortion dissatisfy condition, you can adjust the factory menu item

SCOR CCOR PCAC PCC KEYST PARAL TCC BCC

4.11 O utput the max sound of power

Receive the US-7 signal; adjust the volume to max, check the sound power output no less than 2 x 6W.

4.12 White balance and Horizontal and vertical scanning centre and amplitude adjustment of HDTV

The unit has the YPBPR terminal; it can display the HDTV sig nal Support the HDTV and TIMING of the VG 848 format.

When th e whit e bal an ce ad ju stm ent , t he p ict ur e mod e to STANDARD i n the us er m ode. W hen The H-V scanning adjustment, set the H-CENTER, H-amplitude, V-CENTER and V-amplitude to 0 in the user menu.

4.12.1 YPbPr input (480p signal)

a. Whit e balance adj ustment Input eight level gray of 480p format signal to HDTV YPbPr terminal, the picture mode to ST ANDARD. In the factory menu, select the WHITE BALANCE SETTING menu; adjust the white balance (color temperature to 12000K+/-8MPCD, the color coordinat e t o 0. 270+/-0.008, 0.283+/-0.008). b. H-CENTER adjustment Input white grid of 480p format signal to HDTV YPbPr terminal, t he picture mode to STANDARD. In the factory menu, select Horizontal setting menu, adjust the H POS, until the picture H-center and screen center accord. c. V-CENTER adjustment

S-Correction C-Correction Pin C ushion Asymmetry Correction Pin Cushion Correction Keystone Correction Parallelogram Correction Top Corner Correction Bottom Corner Correction

Support input signal of YPbPr

Signal form at TIMING of the VG848 format

480I 950 480P 978 576I 969

576P 979 1080I/60Hz 972 720P/60Hz 976 1080P/60Hz 970

In the factory menu, select Vert ical setting menu, adjust the V POS, until the picture V-center and screen center accord. d. V-SCANNING adjustment In the factory menu, select Vertical setting menu, adjust the V SIZE, until up and down over scanning of the picture to 8% of the all screen. e. Raster correction and horizontal amplitude adjustment Receive white grid of NTSC signal, the picture mode to “STANDARD” in the factory menu, select horizontal setting menu, adjust the PCC, until the raster distort least, adjust the H SIZE, until right and left over scanning of the picture t o 8% of the all screen. f. If the scanning line distortion and raster geometric distortion dissatisfy condition, you can adjust the factory menu item

SCOR CCOR PCAC PCC KEYST PARAL TCC BCC

4.12.2 YPbPr input (1080I/60Hz format signal) Adjustment mode to 4.12.1

5. Check point

5.1 check the high voltage a. Check the second anode and GND connect to the high voltmeter b. Receive US-7 signal, the picture mode to STANDARD, measure the high voltage to

30.0KV+/-1KV.

c. The brightness and contrast t o m in value, while measure the high voltage no more than 35KV.

5.2 check the CRT Filament voltage Receive the US-7 signal, the picture mode to STANDARD item, measure the CRT filament voltage to be 6.3+/-0.2Vrms.

5.3 Check the X-ray protection a. Receive the US-7 signal, the picture to STANDARD item. b. Connect TP1 to TP2 point of short circuit; X-ray protection cir cuit must be operation.

5.4 Check the picture part

5.5 Check the sub-brightness

5.6 Check chromatic purity and converge

5.7 Check the VIDEO and audio input/out put

5.8 Check the unit and the remote control function

6. Ex-factory pre-setting

7. Check the supply power (AC 100V-140V/60Hz)

S-Correction C-Correction Pin Cushion Asymmetry Correction Pin Cushion Correction Keystone Correction Parallelogram Correction Top Corner Correction Bottom Corner Correction

APPX: horizontal and vertical scanning adjustment diagram

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