LG 1426, SM-20PM Schematic

SERVICE MANUAL

CHASSIS : Mitsubishi DOCUMENT : SM-20PM DATE : 08/08/2005

This manual is the latest at the time of print, and does not include the modification which may be made after the printing, by the constant improvement of product.

CONTENTS

1. Safety precautions…………………………………………………………………………..……………1

2. Service adjustment……………………………………………………………..………………………...2

3. Purity / convergence adjustment……………………………………………………………………..8

4. List of Parts ………………………………………………………………………….…………………….10

5. Circuit Diagram……………………………………………………………………………Attached

1. SAFETY PRECAUTIONS

1. The design of this product contains special hardware, many circuits and components especially for safety purposes. 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. Service should be performed by qualified personnel only.

2. Alterations of the design or circuitry of the products should not be made. Any design alterations or additions will void the manufacturer’s warranty and will further relieve the manufacturer 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 characteristics are often not evident from visual inspection nor can the protection afforded by them necessarily be obtained by using replacement components rated for higher voltage, wattage, etc. Replacement parts which have these special safety characteristics are identified in the parts list of Service manual. Electrical components having such features are identified by shading on the schematics and by ( ！ ) on the parts list in Service manual. The use of a substitute replacement which does not have the same safety characteristics as the recommended replacement part shown in the parts list of Service manual may cause shock, fire, or other hazards

4. Don’ t short between the LIVE side ground and ISOLATED

(NEUTRAL) side ground or EARTH side ground when repairing. Some model’s power circuit is partly different in the

GND. The difference of the GND is shown by the LIVE: ( ) side GND, ISOLATED (NEUTRAL): ( ) side GND and EARTH: ( ) side GND. Don’t short between the LIVE side GND and ISOLATED (NEUTRAL) side GND or EARTH side GND and never measure with a measuring apparatus (oscilloscope etc.) the LIVE side GND and ISOLATED (NEUTRAL) side GND or EARTH side GND at the same time. If above note will not be kept, a fuse or any parts will be broken.

5. If any repair has been made to the chassis, it is recommended that the B1 setting should be checked or adjusted (See ADJUSTMENT OF B1 POWER SUPPLY).

6. The high voltage applied to the picture tube must conform to that specified in Service manual. Excessive high voltage can cause an increase in X-Ray emission, arcing and possible component damage, therefore operation under excessive high voltage conditions should be kept to a minimum, or should be prevented. If severe arcing occurs, remove the AC power immediately and determine the cause by visual inspection (incorrect installation, cracked or melted high voltage harness, poor soldering, etc.). To maintain the proper minimum level of soft X-Ray emission, components in the high voltage circuitry including the picture tube must be the exact replacements or alternatives approved by the manufacturer of the complete product.

7. Do not check high voltage by drawing an arc. Use a high voltage meter or a high voltage probe with a VTVM. Discharge the picture tube before attempting meter connection, by connecting a clip lead to the ground frame and connecting the other end of the lead through a 10kΩ 2W resistor to the anode button.

8. When service is required, observe the original lead dress. Extra precaution should be given to assure correct lead dress in the high voltage circuit area. Where a short circuit has occurred,

those components that indicate evidence of overheating should be replaced. Always use the manufacturer’s replacement components.

9. Isolation Check (Safety for Electrical Shock Hazard) After re-assembling the product, always perform an isolation check on the exposed metal parts of the cabinet (antenna terminals, video/audio input and output terminals, Control knobs, metal cabinet, screw heads, earphone jack, control shafts, etc.) to be sure the product is safe to operate without danger of electrical shock.

10. The surface of the TV screen is coated with a thin film which can easily be damaged. Be very careful with it when handle the TV. Should the TV screen become soiled, wipe it with a soft dry cloth. Never rub it forcefully. Never use any cleaner or detergent on it.

(1) Dielectric Strength Test

The isolation between the AC primary circuit and all metal parts exposed to the user, particularly any exposed metal part having a return path to the chassis should withstand a voltage of 3000V AC (r.m.s.) for a period of one second. (…Withstand a voltage of 1100V AC (r.m.s.) to an appliance rated up to 120V, and 3000V AC (r.m.s.) to an appliance rated 200V or more, for a period of one second.) This method of test requires test equipment not generally found in the service trade.

(2) Leakage Current Check

Plug the AC line cord directly into the AC outlet (do not use line isolation transformers during this check). Using a “Leakage Current Tester”, measure the leakage current from each exposed metal part of the cabinet, particularly any exposed metal part having a return path to the chassis, to a known good earth ground (water pipe, etc.). Any leakage current must not exceed 0.5mA AC (r.m.s.). However, in tropical area, this must not exceed 0.2mA AC (r.m.s.).

●Alternate Check Method Plug the AC line cord directly into the AC outlet ( do not use a line isolation transformer during this check.). Use an AC voltmeter having 1000 ohms per volt or more sensitivity in the following manner. Connect a 1500Ω 10W resistor paralleled by a 0.15μF AC-type capacitor between an exposed metal part and a known good earth ground (water pipe, etc.). 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. Any voltage measured must not exceed 0.75V AC (r.m.s.). This corresponds to 0.5mA AC (r.m.s.). However, in tropical area, this must not exceed 0.3V AC (r.m.s.). This corresponds to 0.2mA AC (r.m.s.)

一、Enter Factory Menu

1） Entrance of factory controller: Use factory key to enter/switch/exit factory mode. Entrance of common

controller: When main menu appears, enter code 6483, which is equivalent to factory key.

2） Specification: Factory mode includes three kinds: FACTORY: for factory aging; B/W BALANCE：for

adjustment of black and white balance; ADJUST：for all adjustments of factory.

Pressing factory key (or pressing 6483 when main menu appears) will display the following:

Common state FACTORY B/W BALANCE ADJUST

二、Factory Explanation

1、 FACTORY (Aging mode): This mode is used for factory aging, in which TV set will not be turned off if

there is no signal.

2、 Adjustment of B/W BALANCE: Press factory key to enter into B/W BALANCE and set value as table 1;

press “MUTE” key to enter horizontal line, and then adjust grid potentiometer to make the horizontal line

to bright up; adjust CUT R, CUT G AND CUT B (See table 2) to make the line turn white; and then adjust

grid potentiometer to make the line disappear. Press “MUTE” key to exit the line and dark balance is OK.

Fine tuning DRI R and DRI B to make the white to become pure white; and B/W BALANCE is OK.

Table 1

OSD

Explanation 14″-21″ 25″-34″

Indication

DRI R

DRI B

CUT R

CUT G

CUT B

BRI

Adjust range of output R （0～127）

Adjust range of output B（0～127）

Adjust base level of output R（0～255）

Adjust base level of output G（0～255）

Adjust base level of output B（0～255）

Adjust brightness of horizontal line（0~255）

60 60

63 63

100 100

108 120

SIG 8 second built-in signal

Table 2

Key Name 1 2 3

Function CUT R+ CUT G+ CUT B+

Key Name 4 5 6

Function CUT R- CUT G- CUT B-

Note: BRI is only for adjusting voltage of grid, not for SUB-brightness; so please set BRI value as the

above table. It is better not to make any changes. If it needs to make change, please make it within the

range 14″-21″：100-120；25″-34″：110-130.

3、 ADJUSTMENT

Explanation of adjustments and settings: There are 11 pages for adjustments and settings from “SERVCJ0”

to “SERVCJ9” and “AUTO VCJ”. It is available to turn down the page with MUTE key and swiftly arrive the

set page with 0-9 keys. Use P+/P- to select the adjusted item; and use VOL+ or VOL- to make set

adjustment.

0) Page SERVCJ0

No. Name Explanation

0 H PH Line center (range: 0~31)

1 V SH Vertical center (range: 0-7)

2 V SI Vertical range (range: 0-63)

3 V SC Vertical correction SC (range: 0-63) (effective only when choosing

M61264)

4 V LI Vertical linearity (range: 0-63) (effective only when choosing M61264)

5 N H PH Deviation amount of line center in NTSC (range: -31~+31)

6 N V SH Deviation amount of vertical center in NTSC (range: -7~+7)

7 N V SI Deviation amount of line center in NTSC (range: -63~+63)

8 N V SC Deviation amount of vertical correction SC in NTCS (range: -63~+63)

(effective only when choosing M61264)

9 N V LI Deviation amount of vertical linearity in NTCS (range: -63~+63)

(effective only when choosing M61264)

1) SERVCJ1

No. Name Explanation 30

0 AGC RF.AGC adjustment (range: 0~127) 1

1 H T Half-transparent switch (0: off; 1: on)

2 AUDIO Audio output (range: 0~127); effective only when the value of PWM

100

OPT of SERVCJ4 is more than 0.

3 YDL

Time delay adjustment of brightness（0～7）

4 VDL V delay adjustment L (0~3) (effective only in YUV mode) 0

5 UDL U delay adjustment (0~3) (effective only in YUV mode) 0

6 YUV TINT

YUV tincture adjustment （0~127）(effective only in YUV mode)

2) Page SERVCJ2 (effective only in M61260)

No. Name Explanation

0 S BL R

1 S BL B

2 S YDL

3 S BPG

Adjustment of SECAM R-Y signal（0～31）

Adjustment of SECAM B-Y signal（0～31）

Time delay compensation of SECAM（ 0：off 1：on）

Time delay option of SECAM BGP（0～3）

3）Page SERVCJ3

No. Name Explanation

0 IC Option of decoding CMOS chip (M61260/M61264/M61266) M61264

1 SEA CHACK

Checking of automatic channel searching when TV set is turned on.（0：

no 1：yes）

2 CAL

3 GAME

4 ZOOM

5 LOCK

6 CURT

7 WOO

8 SAVER

Option of calendar (1：yes/ 0：no)

Option of game (0：no /1: yes)

Option of ZOOM (1：yes/ 0：no)

Option of child lock (1：yes/ 0：no)

Option of

screen stretching (0：no / 1：on / 2：off / 3：both)

Option of bass（0：no 1: base switch 2：digital control）

Option of screen protection (0：no 1：yes 2：uper line LOGO 3: two line

LOGO)

4）Page SERVCJ4

0 HP Left/right of OSD (range: 0~60) 28

1 VP Up/down of OSD (range: 0~60) 29

2 Z1 Vertical range data when screen is enlarged (range: 0~63) 58

3 Z2 Vertical range data when screen is widened (range: 0~63) 30

4 CURT TIM Time option of black screen before stretching screen when TV set is turned on

(range: 0~30 seconds)

5 PWM Volume option (0: inner volume control;, 1: 1-circuit PWM output; 2:2-circuit

PWM number, 3: IC control of acoustics)

6 AV

AV option （0：1-circuit AV 1: 2-circuit AV 2：1-circuit AV, 1-circuit YUV

3: 2-circuit AV，1-circuit YUV）

7 S SYS Option of sound system (see note 1) 01111

8 POW

Option of turning-on state (（0：direct turning on 1：turning on after standby 2：

memory turning on）

Note 1: display 0

0 0 0 0

D/K

5.742

As shown in the fig., the sound will be opened when each of the corresponding sound system is in 1 position;

and closed when in 0.

5）Page SERVCJ5

0 V FREQ

Option of middle frequency: 38.0MHZ、38.9MHZ、39.5MHZ、45.75MHZ、

38.0

34.47MHZ

1 V VCO Tuning of middle frequency: when tuning, AFT of the last line in the menu is in

OK mode.

2 V GAIN

Scale control of video output（0~7）

3 H VCO Tuning of horizontal frequency (range: 0~7) 3

4 C TR

limiting of color waves（0 ~ 3）(ineffective when tuning in terminal S or YUV input)

6）Page SERVCJ6

0 BS SW

1 BS CHAG

2 BS DIS

3 BS GAIN

4 GAMMA

5 A SW

black level extending switch: 0：on/1：off

（0～3）controlling of extending scale of black level（0～3）

Gaining switch of black level extending: 0：normal、1：enhance

（0~3）Correction of curve GAMMA（0~3）

limiting switch of automatic contrast: 0：control of automatic contrast, 1：

limiting of automatic contrast.

6 A GAIN

7 OM DET

8 M/N

ABCL gaining switch 0：low, 1：high

Checking of modulation: 0：off, 1：on

ption of PAL-N，PAL-M 0：off, 1：on

7）Page SERVCJ7

0 D OSD

1 OSD L

2 S DOWN

3 R MIX

4 VSY DET

OSD digit 1：off 0：on

Output scale of OSD digit: 0：low 1：high

Sync cutting mode: 0: 50％, 1: 40％, 2: 30％, 3: 25%

Adjustment of matrix R: 0：normal 1：enhance

Switch of sync time testing: 0：11.5us 1：20.5us

5 BLACK SCR Option of screen blackening 1

6 VOL CHOICE

Option of acoustics curves: 0：standard 1：customer

8）Page SERVCJ8

0 SUB CONT Sub-contrast 0~29 18

1 SUB BRI Sub-brightness 0~105 20

2 SUB COL Sub-color 0~27 18

3 SUB SHA Sub-sharpness 0~13 13

4 SUB TI Sub-tincture 0~27 10

5 SA BR Screen protection and brightness of blueness in no-signal mode 0~255 138

6 LAN CHOICE Language option: 0: only English, 1: Chinese, English 1

7 TUNER

TUNER OPTION: 0：VS TUNER, 1: FS TUNER

CHOICE

9）Page SERVCJ9 (effective only in choosing M61266)

0 Cr ADJ

1 Cb ADJ

2 SIF45 GAIN

3 SIF PAL

4 SIF PAL INV

5 AMF

Adjustment of base level Cr （0~15）

Adjustment of base level Cb （0~15）

Attenuation of output scale of NTSC acoustics （0：0dB 1：-6dB）

enhancing of PAL SNR（0：OFF 1: ON）

Polarity switch of SIF PAL（0: NORMAL 1: INVERT）

Testing switch of weak radio-frequency signal（0：OFF 1:ON）

6 AMF VTH Level adjustment of weak radio-frequency signal testing

7 AMF CUR

reduce filtering current of MF AGC（0: NORMAL 1: CURRENT

REDUCED）

8 AMF HYS

Switch HYS （0: OFF 1: ON）

10）Page AUTO VCJ: This menu automatically adjusts VIF VCO and S TRAP; and save the adjusted data in

EEPROM. Pressing volume key begins the automatic adjustment and it will return to original mode 2~3

seconds after adjustment.

Note 1: the adjusted datum will be shown in SER VCJ5.

Note 2: Adjusting will not affect any keys.

0 S TRAP

1 VIF VCO

三、Explanation of Special Function

1． Enter factory LOG set: press “LOGO” key will directly enter into adjusting mode; or in “AV” indication for

common controller in AV state, successively input 6483 will also enter into adjusting mode.

2、Setting of factory LOGO: There are two lines for factory LOGO, the 1

defined by customer; the 2

of which is for customer to define (it is available for customer to set not more

of which is “Double Happiness” or

than 13 characters). And customer may set switch, font, color, up/down position and left/right position. If

“LOGO” in the menu is set in “ON” position, the screen will show the equivalent “LOGO” when there is on

signal in POWER-ON state.

• The setting menu of factory logo is displayed on two screens, which are available to adjust the 1

line and 2

line of the LOGO separately. After entering the setting menu, press POS+/POS to

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