Akai 25CT23FSR, 29CT23FSR Schematic

COLOUR TV SET

Models: 25CT23FSR 29CT23FSR

SERVICE MANUAL

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SERVICE MANUAL

TABLE OF CONTENTS

TABLE OF CONTENTS................................................................................................... 1

SAFETY INSTRUCTIONS AND MAINTENANCE......................................... 2

X-RAY RADIATION PRECAUTION.......................................................................................... 2

SAFETY PRECAUTION.............................................................................................................. 2

PRODUCT SAFETY NOTICE .................................................................................................... 3

SAFETY SYMBOL DESCRIPTION........................................................................................... 3

MAINTENANCE............................................................................................................................ 4

ADJUSTMENTS .................................................................................................................. 5

SET-UP ADJUSTMENTS ........................................................................................................... 5

CIRCUIT ADJUSTMENTS.......................................................................................................... 8

STRUCTURE AND CHASSIS FUNCTION DESCRIPTION..................... 14

STRUCTURE BLOCK DIAGRAM ............................................................................................. 14

BLOCK DIAGRAM FOR SUPPLY VOLTAGE SYSTEM ...................................................... 15

CHASSIS DESCRIPTION ...........................................................................................................16

SERVICE DATA ..................................................................................................................17

TECHNICAL DATA OF KEY ICS ...............................................................................................17

WAVEFORMS OF KEY POINTS ...............................................................................................35

SERVICE DATA OF KEY ICS ....................................................................................................38

REPLACEMENT OF PARTS .......................................................................................44

APPENDIX

1. CIRCUIT DIAGRAM

INSTRUCTIONS FOR SERVICE SAFETY AND MAINTENANCE

WARNING: BEFORE SERVICING THIS CHASSIS, READ THE X-RAY

RADIATION PRECAUTION , SAFETY PRECAUTION AND PRODUCT

SAFETY NOTICE INSTRUCTION BELOW.

X-RAY RADIATION PRECAUTION

1. The EHT must be checked every time the TV is serviced to ensure that the CRT does not emit

X-ray radiation as result of excessive EHT voltage. The maximum EHT voltage permissible in

any operating circumstances must not exceed the rated value. When checking the EHT, use

the High Voltage Check procedure in this manual using an accurate EHT voltmeter.

2. The only source of X-RAY radiation in this TV is the CRT. The TV minimizes X-RAY radiation,

which ensures safety during normal operation. To prevent X-ray radiation, the replacement

CRT must be

3. Some components used in this TV have safety related characteristics preventing the CRT from

emitting X-ray radiation. For continued safety, replacement component should be made after

referring the PRODUCT SAFETY NOTICE below.

4. Service and adjustment of the TV may result in changes in the nominal EHT voltage of the

CRT anode. So ensure that the maximum EHT voltage does not exceed the rated value after

service and adjustment.

identical to the original fitted as specified in the parts list.

SAFETY PRECAUTION

WARNING: REFER SERVICING TO QUALIFIED SERVICE PERSONNEL ONLY.

1. The TV has a nominal working EHT voltage. Extreme caution should be exercised when

working on the TV with the back removed.

1.1 Do not attempt to service this TV if you are not conversant with the precautions and procedures

for working on high voltage equipment.

1.2 When handling or working on the CRT, always discharge the anode to the TV chassis before

removing the anode cap in case of electric shock.

1.3 The CRT, if broken, will violently expel glass fragments. Use shatterproof goggles and take

extreme care while handling.

1.4 Do not hold the CRT by the neck as this is a very dangerous practice.

2. It is essential that to maintain the safety of the customer all power cord forms be replaced

exactly as supplied from factory.

3. Voltage exists between the hot and cold ground when the TV is in operation. Install a suitable

isolating transformer of beyond rated overall power when servicing or connecting any test

equipment for the sake of safety.

4. When replacing ICs, use specific tools or a static-proof electric iron with small power (below

35W).

5. Do not use a magnetized screwdriver when tightening or loosing the deflection yoke assembly

to avoid electronic gun magnetized and decrement in convergence of the CRT.

6. When remounting the TV chassis, ensure that all guard devices, such as nonmetal control

buttons, switch, insulating sleeve, shielding cover, isolating resistors and capacitors, are

installed on the original place.

7. Replace blown fuses within the TV with the fuse specified in the parts list.

8. When replacing wires or components to terminals or tags, wind the leads around the terminal

before soldering. When replacing safety components identified by the international hazard

symbols on the circuit diagram and parts list, it must be the company-approved type and must

be mounted as the original.

9. Keep wires away from high temperature components.

PRODUCT SAFETY NOTICE

CAUTION: FOR YOUR PROTECTION, THE FOLLOWING PRODUCT SAFETY NOTICE

SHOULD BE READ CAREFULLY BEFORE OPERATING AND SERVICING THIS TV SET.

1. Many electrical and mechanical components in this chassis have special safety-related

characteristics. These characteristics are often passed unnoticed by a visual inspection and

the X-ray radiation protection afforded by them cannot necessarily be obtained by using

replacements rated at higher voltages or wattage, etc. Components which have these special

safety characteristics in this manual and its supplements are identified by the international

hazard symbols on the circuit diagram and parts list. Before replacing any of these components

read the parts list in this manual carefully. Substitute replacement components which do not

have the same safety characteristics as specified in the parts list may create X-ray radiation.

2. Do not slap or beat the cabinet or CRT, since this may result in fire or explosion.

3. Never allow the TV sharing a plug or socket with other large-power equipment. Doing so may

result in too large load, causing fire.

4. Do not allow anything to rest on or roll over the power cord. Protect the power cord from being

walked on, modified, cut or pinched, particularly at plugs.

5. Do not place any objects, especially heavy objects and lightings, on top of the TV set. Do not

install the TV near any heat sources such as radiators, heat registers, stove, or other

apparatus that produce heat.

6. Service personnel should observe the SAFETY INSTRUCTIONS in this manual during use and

servicing of this TV set. Otherwise, the resulted damage is not protected by the manufacturer.

SAFETY SYMBOL DESCRIPTION

The lightning symbol in the triangle tells you that the voltage inside this product

may be strong enough to cause an electric shock. Extreme caution should be

exercised when working on the TV with the back removed.

This is an international hazard symbol, telling you that the components identified

by the symbol have special safety-related characteristics.

FDA This symbol tells you that the critical components identified by the FDA marking

have special safety-related characteristics.

UL This symbol tells you that the critical components identified by the UL marking

have special safety-related characteristics.

C UL This symbol tells you that the critical components identified by the C-UL marking

have been evaluated to the UL and C-UL standards and have special

safety-related characteristics.

VDE This symbol tells you that the critical components identified by the VDE marking

have special safety-related characteristics.

MAINTENANCE

1. Place the TV set on a stable stand or base that is of adequate size and strength to prevent it

from being accidentally tipped over, pushed off, or pulled off. Do not place the set near or

over a radiator or heat register, or where it is exposed to direct sunlight.

2. Do not install the TV set in a place exposed to rain, water, excessive dust, mechanical

vibrations or impacts.

3. Allow enough space (at least 10cm) between the TV and wall or enclosures for proper

ventilation.

4. Slots and openings in the cabinet should never be blocked by clothes or other objects.

5. Please power off the TV set and disconnect it from the wall immediately if any abnormal

condition are met, such as bad smell, belching smoke, sparkling, abnormal sound, no

picture/sound/raster. Hold the plug firmly when disconnecting the power cord.

6. Unplug the TV set from the wall outlet before cleaning or polishing it. Use a dry soft cloth for

cleaning the exterior of the TV set or CRT screen. Do not use liquid cleaners or aerosol

cleaners.

ADJUSTMENTS

SET-UP ADJUSTMENTS

The following adjustments should be made when a complete realignment is required or a new

picture tube is installed.

Perform the adjustments in the following order:

1. Color purity

2. Convergence

3. White balance

Notes:

The purity/convergence magnet assembly and rubber wedges need mechanical

positioning. Refer to Fig1, 2.

For some picture tubes, purity/ convergence adjustments are not required.

1. Color Purity Adjustment

Preparation:

Before starting this adjustment, adjust the vertical sync, horizontal sync, vertical amplitude and

focus.

1.1 Face the TV set north or south.

1.2 Connect the power plug into the wall outlet and turn on the main power switch of the TV set.

1.3 Operate the TV for at least 15 minutes.

1.4 Degauss the TV set using a specific degaussing coil.

1.5 Set the brightness and contrast to maximum.

1.6 Counter clockwise rotate the R /B low brightness potentiometers to the end and rotate the

green low brightness potentiometer to center.

1.7 Receive green raster pattern signals.

1.8 Loosen the clamp screw holding the deflection yoke assembly and slide it forward or backward

to display a vertical green zone on the screen. Rotate and spread the tabs of the purity magnet

around the neck of the CRT until the green zone is located vertically at the center of the screen.

1.9 Slowly move the deflection yoke assembly forward or backward until a uniform green screen is

obtained.

1.10 Tighten the clamp screw of the assembly temporarily. Check purity of the red raster and blue

raster until purities of the three rasters meet the requirement.

2. Convergence Adjustment

Preparation:

Before attempting any convergence adjustment, the TV should be operated for at least 15

minutes.

2.1 Center convergence adjustment

2.1.1 Receive dot pattern.

2.1.2 Adjust the brightness/contrast controls to obtain a sharp picture.

2.1.3 Adjust two tabs of the 4-pole magnet to change the angle between them and red and blue

vertical lines are superimposed each other on the center of the screen.

Yok

Fig. 1

2.1.4 Turn both tabs at the same time keeping the angle constant to superimpose red and blue

horizontal on the center of the screen.

2.1.5 Adjust two tabs of the 6-pole magnet to superimpose red/blue line and green line.

2.1.6 Remember red and blue movement. Repeat steps 2.1.3 2.1.5 until optimal convergence is

obtained.

2.2 Circumference convergence adjustment

2.2.1 Loosen the clamp screw holding the deflection yoke assembly and allow it tilting.

2.2.2 Temporarily put the first wedge between the picture tube and deflection yoke assembly.

Move front of the deflection yoke up or down to obtain better convergence in circumference.

Push the mounted wedge in to fix the yoke temporarily.

2.2.3 Put the second wedge into bottom.

2.2.4 Move front of the deflection yoke to the left or right to obtain better convergence in

circumference.

2.2.5 Fix the deflection yoke position and put the third wedge in either upper space. Fasten the

deflection yoke assembly on the picture tube.

2.2.6 Detach the temporarily mounted wedge and put it in either upper space. Fasten the

deflection yoke assembly on the picture tube.

2.2.7 After fastening the three wedges, recheck overall convergence and ensure to get optimal

convergence. Tighten the lamp screw holding the deflection yoke assembly.

3. White Balance Adjustment

Generally, white balance adjustment is made with professional equipment. It’s not practical to

get good white balance only through manual adjustment. For TVs with I2C bus control, change

the bus data to adjust white balance.

Fig. 2

4-pole Magnet Movement 6-pole Magnet Movement

Center Convergence by Convergence Magnets

Incline the Yoke Up (or Down) Incline the Yoke Right (or Left)

Circumference Convergence by DEF Yoke

Fig.3

CIRCUIT ADJUSTMENTS

Preparation:

Circuit adjustments should be made only after completion of set-up adjustments.

Circuit adjustments can be performed using the adjustable components inside the TV set. For TVs

with I

C bus control, first change the bus data.

1. Degaussing

A degaussing coil is built inside the TV set. Each time the TV is powered on, the degaussing

coil will automatically degauss the TV. If the TV is magnetized by external strong magnetic field,

causing color spot on the screen, use a specific degausser to demagnetize the TV in the

following ways. Otherwise, color distortion will be shown on the screen.

1.1 Power on the TV set and operate it for at least 15 minutes.

1.2 Receive red full-field pattern.

1.3 Power on the specific degausser and face it to the TV screen.

1.4 Turn on the degausser. Slowly move it around the screen and slowly take it away from the TV.

1.5 Repeat the above steps until the TV is degaussed completely.

2. Confirmation and Adjustment for Voltage

Caution: +B voltage has close relation to high voltage. To prevent X-ray radiation, set +B

voltage to the rated value.

2.1 Power on the TV and receive Philips test pattern.

2.2 Check the resistors and coils for being burned. (If the fuse is burned out, do not power on the

TV again until the cause is found out.)

2.3 Measure voltages of test points with the digital voltmeter. Measure the CRT high voltage with

the high-voltage testing equipment and heater voltage with the high-frequency effective

voltmeter. The rated values are shown as table 2.

Table 2

Test Point Voltage (V)

Negative of VD831 145 1.5V

Negative of VD461B 12 1V

Negative of VD832 15 1V

Positive of C462 17 1V

Positive of C452 47 3V

Positive of C492 195 5V

Heater 6.3 0.3Vrms

CRT 28.8KV 1KV

3. High Voltage Inspection

Caution: No high voltage adjustment components inside the chassis. Please perform

high voltage inspection in the following ways.

3.1 Connect a precise static high voltmeter to the second anode (inside the high voltage cap) of the

CRT.

3.2 Plug in the supply socket (150-250V ~, 50Hz) and turn on the TV. Set the brightness and

contrast to minimum (0 A).

3.3 The high voltage reading should be less than the limited EHT voltage.

3.4 Change the brightness from minimum to maximum, and ensure high voltage not beyond the

limitation in any case.

Nominal EHT voltage: 28.8KV 1KV Limited EHT voltage: 32KV

4. Focus Adjustment

Caution: Dangerously high voltages are present inside the TV. Extreme caution should

be exercised when working on the TV with the back removed.

4.1 After removing the back cover, look for the FBT on the main PCB. There should be a FCB on

the FBT.

4.2 Power on the TV and preheat it for 15 min.

4.3 Receive a normal TV signal. Rotate knob of the FCB until you get a sharp picture.

Before Adjusting After Adjusting

Fig. 4

5. Safety Inspection

5.1 Inspection for insulation and voltage-resistant

Perform safety test for all naked metal of the TV. Supply high voltage of 3000V, 50Hz (limit

current of 10mA) between all naked metal and cold ground. Test every point for 3 sec. and

ensure no arcing and sparking.

5.2 Requirements for insulation resistance

Measure resistance between naked metal of the TV and feed end of the power cord to be

infinity with a DC-500 high resistance meter and insulation resistance between the naked metal

and degaussing coil to be over 20M .

6. SERVICE mode

6.1 To enter the SERVICE mode

Set the volume to 0 by the remote control. Then press and hold the MUTE button on the

remote control and MENU button on the TV at the same time for over 2 seconds. In the S mode,

press the POWER button to quit the S mode.

( S is red and other items are yellow.)

Use the / buttons on the remote control to highlight an adjustment and the / buttons

to adjust it.

The POS+/-, / / / ,1~6, RECALL, VOL+/-, MUTE and POWER buttons on the remote

control function in the S mode, but 100+, 7, 8, 9 and 0 buttons not.

6.2

Bus data

Table 3 Bus data

Data in S

Mode

OP1 7B Option set byte 1 See Table 4

OP2 48 Option set byte 2 See Table 4

OP3 FF Option set byte 3 See Table 4

OP4 F5 Option set byte 4 See Table 4

OP5 36 Option set byte 5 See Table 4

OP6 28 Option set byte 6 See Table 4

AVG Vertical output

INIT Initializing E2PROM

TAB Data check sheet See Table 5

VX00 19 4:3

VX50 01 16:9

VX99 38 Zoom

VS Set to the optimum Half vertical output

VA Set to the optimum

SC Set to the optimum S correction

VSH Set to the optimum

5OV Set to the optimum

HP Set to the optimum Parallelogram correction

HB Set to the optimum Bow correction

5HS Set to the optimum

5HA Set to the optimum

Adjustment Description

Vertical amplitude (When vertical frequency is identified to

50Hz, “5VA” is displayed when identified to 60Hz, “6VA”

displayed.)

Vertical shift (When vertical frequency is identified to 50Hz,

“5VSH” is displayed when identified to 60Hz, “6VSH”

displayed.)

Character field starting position (When vertical frequency is

identified to 50Hz, “5OV” is displayed when identified to

60Hz, “6OV” displayed.)

Horizontal shift (When vertical frequency is identified to

50Hz, “5HS” is displayed when identified to 60Hz, “6HS”

displayed.)

Horizontal amplitude (When vertical frequency is identified to

50Hz, “5HA” is displayed when identified to 60Hz, “6HA”

displayed.)

( continued )

East-west pincushion correction (When vertical frequency is

5EW Set to the optimum

UCP Set to the optimum Upper corner correction

BCP Set to the optimum Bottom corner correction

TC Set to the optimum Trapezoidal correction

RCUT Set to the optimum Red gun cutoff voltage

GCUT Set to the optimum Green gun cutoff voltage

RDRV Set to the optimum Red gun drive voltage

GDRV Set to the optimum Green gun drive voltage

BDRV 20 Blue gun drive voltage

YDFP 0D Brightness delay PAL

YDFN 0D Brightness delay NTSC

YDFS 0D Brightness delay SECAM

YDAV 0D AV brightness delay

AGC Set to the optimum Automatic gain control (AGC)

VOL 28 Volume initial value

IFFS O3 Intermediate frequency

CL OB

AGCS 03 AGC speed

VG2B 30 VG2 brightness

SVOL 36 Volume 00

MVOL 3C Volume 25

SBRI 1F Sub brightness

MBRI 33 Brightness Max.

SCON 0C Sub contrast

MCON 3F Contrast Max.

MCOL 3F Color Max.

identified to 50Hz, “5EW” is displayed when identified to

60Hz, “6EW” displayed.)

OP1

Table 4 Option bit setting

Bit Item Description

0 OP_HOTEL Hotel Mode: 1: Yes, 0: No

1 OP_HWSN Audio processor: 1: TDA9859, 0: No

2 OP_SUPERWOOFER Super woofer: 1: Yes, 0: No

3 OP_NTSC NTSC option: 1: Yes, 0: No

4 OP_AV2 1: With AV2; 0: Without AV2

5 OP_SVHS S-Video: 1: Yes, 0: No

6 OP_DVD DVD 1: Yes, 0: No

( continued )

7 OP_RGB RGB 1: Yes, 0: No

0 OP_AVL AVL 1: Yes, 0: No

OP2

OP3

1 OP_AUTO_SOUND

2 OP_KEY

3 OP_OSO Switch off in vertical overscan

4 OP_NOT_3 National option (disabled)

5 OP_USER_LOGO User write-in logo option (prior to Changhong logo)

6 OP_ON_BACK Power-on auto-test background: 1: Blue, 0: Black

7 OP_FSL Slicing level for vertical sync

0 OP_ENGLISH English

1 OP_FARSI Farsi

2 OP_ARABIC Arabic

3 OP_RUSSIAN Russian

4 OP_FRENCH French

5 OP_GERMAN German

6 OP_ITALY Italian

uto sound system test: 1:Yes, 0: No

Key: 1: Standard 0: Non-standard

OP4

OP5

7 OP_SPAIN Spanish

Window selection of sound PLL:

0 OP_FMWS

1: Large window, 0: Small window

OP_DIRECT_SWITCH_ONMemory on: 1: Remote on if remote off; instant on if

AC off 0: Soft on

2 OP_HCO EHT: EW control 1:On 0: Off

Changhong logo display

3 OP_CHH_LOGO

1: Yes under no signal condition 0: No

4 OP_SOUND_DK Audio system DK option: 1: Yes, 0: No

5 OP_SOUND_BG Audio system BG option: 1: Yes, 0: No

6 OP_SOUND_I Audio system I option: 1: Yes, 0: No

7 OP_SOUND_M Audio system M option: 1: Yes, 0: No

0 OP_TUNER Tuner 1: Philips tuner, 0: Panasonic tuner

1 OP_AUTO_LANG0

Auto language option: English - Farsi - Arabic -

2 OP_AUTO_LANG1

Russian - French - German - Italian – Spanish, for

( continued )

example:

OP6

3 OP_AUTO_LANG2

4 OP_FORF

5 OP_FORS

6 OP_AV_ON

7 OP_HOTEL_ON_PROG

0 OP_AUTOTEST Power-on auto test: 1: Yes, 0: No

1 OP_PSNS Sensitivity

2 OP_BSCREEN Black screen when changing channels 1: Yes 0: No

3 OP_SECAM SECAM option: 1: Yes, 0: No

4 OP_DFL Disable flash protection

LANG2 /LANG1/ LANG0

0/0/0”: English, “0/0/1”: Farsi

Vertical frequency (OP_FORS/FORF): 00-Auto (60Hz

under no signal condition), 01-KeepLast,

10-Force60Hz, 11-Auto (50Hz under no signal

condition)

1: The former mode before power-off when power-on

0: TV mode when power-on

Fixed to Channel 1 when power-on Activated with

OP-HOTEL 1: Yes, 0: No

Notes:

5 OP_SIF SIF selection 1: External, 0: Internal

6 OP_EXT_SIF0

7 OP_EXT_SIF1

Table 5 TAB data check sheet

OP1 OP2 OP3 OP4 OP5 OP6

VX00 YD( FP/FN/FS/ AV) AGC I FFS CL AGCS

VOL VG2B SVOL MVOL

SBRI MBRI SCON MCON MCOL

RCUT GCUT RDRV GDRV BDRV

The data sheet may differ dependent on different models.

The data sheet may differ dependent on different CRTs for the same model.

External circuit sound system selection (SIF1/SIF0)

00: DK, 01: BG, 10: I, 11: M

Activated with OP-SIF

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