NEC PF-68T31 Schematic

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COLOUR TELEVISION

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PF-68T31

PF-68V21

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TV/AV

P+

V- MENU V+

CALL P-

SLEEP LOCK

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ZOOM

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RE-001

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CONTENTS

z SPECIFICATIONS …………………………………………………………………….. 2 z SAFETY PRECAUTIONS …………………………………………………………….. 3 z SERVICE ADJUSTMENTS …………………………………………………………… 7 z PARTS LIST …………………………………………………………………………… 19 z STANDARD CIRCUIT DIAGRAM

SPECIFICATIONS

Item Specifications

.

Dimensions(W x H x D) Weight

TV RF System

Colour System

TV Mode

Video Mode

Receiving Frequency

VHF (VL) VHF (VH)

UHF

CATV None

Intermediate Frequency

VIF Carrier SIF Carrier

Colour Sub Carrier Frequency Aerial Input Terminal

Power Input Rated Voltage

730 mm x 590 mm x 520 mm

49.5 kg

B/G

PAL

PAL/ NTSC 3.58/ NTSC 4.43

46.25 MHz to 168.25 MHz

175.25 MHz to 463.25 MHz

471.25 MHz to 863.25 MHz

38.9 MHz

33.4 MHz

PAL (4.43 MHz)

75 Ohm Unbalanced DIN

240 V AC, 50/60 Hz

Power Consumption

Picture Tube

High Voltage

Speaker Audio Output Input

Video

Audio

Output

Video Audio Headphone jack

Remote Control Unit

Design & specifications are subject to change without notice.

145 W (Max.)

Visible Size: 68 cm measured diagonally

30 kV ±1.5 kV (at Zero beam current)

8 cm x 13 cm Oval x 2

8 W + 8 W

1 Vpp, 75 Ohm, RCA x 2

S-Video Input Y, C

Components Input Y, Cb, Cr (PF-68T31)

500 mVrms (-4dBs), High impedance, RCA x 4

1 Vpp, 75 Ohm, RCA x1

500mVrms (-4dBs), Low impedance, RCA x 2 Stereo Mini jack (φ3.5mm)

RE-002 (PF-68V21), RE-003 (PF-68T31)

(Battery size: AAA/R03/UM-4 x 2)

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SAFETY PRECAUTIONS

1. The design of this product contains special hardware, many circuits and components specially 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 (

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 with 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 resitor 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.



) on the parts list in Service manual. The use

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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, screwheads, earphone jack, control shafts, etc.) to be sure the product is safe to operate without danger of electrical shock.

(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 periode of one second.) This method of test requires a 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 a line isolation transformer 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 1500 Ω 10W resistor

paralleled by a 0.15 μ F 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.)

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EXPLODED VIEW PF-68T31/PF-68V21

FRONT CABINET

CRT PWB

CONTROL PWB

SPEAKER &

SPEAKER BOX

-

STEREO PWB PF-68T31

REAR TERMINAL

BOARD

POWER PWB

MAIN PWB

REAR CABINET

AC POWER CORD

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REPLACEMENT OF MEMORY IC

1. MEMORY IC.

This TV uses memory IC. In the memory IC are memorized data for correctly operating the video

and deflection circuits.

When replacing memory IC, be sure to use IC written with the initial value of data.

2. PROCEDURE FOR REPLACING MEMORY IC

(1) Power off

Switch the power off and unplug the power cord from AC outlet.

(2) Replace IC

Be sure to use memory IC written with the initial data values.

(3) Power On

Plug the power cord into the AC outlet and switch the power On.

(4) Check and set SYSTEM default value:

1) Press “TEST” key on the special service use Remote control unit.

2) The “TEST” will be displayed on the screen.

3) Press “0” to “8“ key, (Mkey) and corresponding on-screen display will be appeared.

4) In this section, except “3”, “4” and “5” key function would be confirmed.

5) Check the setting value of the SYSTEM default value of Table 1. If the value is different,

select items by [CH+]/[CH-] keys and set value by [VOL+]/[VOL-] keys.

6) Press “TEST” key again and return to the normal screen.

SERVICE ADJUSTMENT

B1 POWER SUPPLY

1. Receive normal colour bar signal.

2. Connect DC voltmeter to TP91 and isolated ground.

3. Adjust VR651 to get the voltage as 130V ±1.0V.

FOCUS ADJUSTMENT

1. Receive a crosshatch signal.

2. While watching the screen, adjust the FOCUS VR to make the vertical and horizontal lines as

fine and sharp as possible.

STEREO ADJUSTMENT (PF-68T31)

1. Receive A2 stereo signal.

2. Adjust L3101 to get the voltage at TP1 (N3101 Pin #3) as 2.5V ±0.1V

3. Adjust VR3101 to get same amplitude at TP3 and TP4.

BUS CONTROL ADJUSTMENT

To enter BUS control mode, use special remote control with “TEST” key, and push “TEST” key.

On TV screen “TEST” will be indicated, this means entered bus control mode.

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And press following key, each function will be available.

Remote Hand Unit keys

[M1] [M2] [M3] [M4]

1 2 3 4

[M5] [M6] [M7]

5 6 7 8

[M0]

9 0

[M4] menu

MENU4 Geometrical adjustment

Receive PAL standard Complete pattern signal.

Adjustment steps：

a) Adjust V. SLOPE, to the center horizontal line just appeare from half bottom shadow.

b) Adjust V-SHIFT, the center horizontal line correspond to CRT vertical center.

c) Adjust V-AMPL, to get 90% of vertical picture contents would be displayed on CRT.

[M5] menu

a) Adjust H-SHIFT, to get the picture horizontal center correspond to CRT horizontal center.

b) Adjust H-AMP, to get 90% of horizontal picture contentswould be displayed on CRT.

c) Adjust H-PARABORA, to get minimum side pincushion distortion.

d) Adjust CORNER, to get minimum distortion of 4-corners.

e) Adjust TRAPEZ, to get minimum trapezoid distortion.

Receive NTSC signal and repeat above [M4] and [M5] adjustment.

[M2] Menu

RF AGC Adjustment.

Receive 60dBμ(1mV)V

noise reduce gradually and just disappeared point.

[M3] Menu

CRTcut off and white balance adjustment.

Receive white signal.

a) CRT cut off adjustment.

1. Select “SC”, then automatically vertical scan will be stopped.

2. Adjust SCREEN control on Flyback transformer to get the darkest single horizontal line

(red, green, or blue, sometimes shows more yellow, more purple or more white).

3. Using (above) 1、2，5、6, 9, 0 keys, to get one white horizontal bar. Then re-adjust

SCREEN control to get horizontal bar would be just visible.

b) White balance adjustment.

1. Select WR/WB menu.

2. Adjust WR/WB to get colour temperature as x=281, y=311

colour bar pattern signal，adjust AGC value（voltage from high to low），to

H

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c) Sub-Brightness adjustment. (Use stair case signal)

1. Select SB menu.

2. Adjust SB to get the darkest step being cutoff.

Default Settings

Mkey ITEMS VARIABLE RANGE DEFAULT

M0

M1

M2

M3 C

M4

PAL

NTSC 3.58

NTSC 4.43

SECAM

D/K

I

B/G

M

Headphone CPU Vol Band Mode Search Speed Power ON BUS Stop(Open)

Shipping RF AGC Delay Y-Delay

Sound Volume

Sub-Sharpness

Sub-Colour

IF Freq.

AV Mode

BR

CT

SC

WR

WG

WB

SB

V.SLOPE

V.SHIFT

V.AMPL

S.CORR

0 →1

0 → 1

0 → 1 0 →1 0 → 1 0 → 1

0 → 1

0 → 63 0 → 15

0 → 63

0 → 5

0 → 7

0 → 100

0 → 63

1

0

1

0

1 0 1 0 0 0

0

6

7

46 (PF-68V21)

47 (PF-68T31

50

38.9

4 (PF-68V21)

5 (PF-68T31)

6

20

75

45

50

PAL NTSC

32

29

30

21

32

28

31

7

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H-SHIFT

H-AMPL

H-PARABORA

CORNER

TRAPEZ

M6 OSD-H

OSD-V

M7

V. AMPL1

V. AMPL2

0 → 63

0 → 29

0 → 38

PAL NTSC M5

39

53

23

30

32

2

1

9

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ICs functional description

3.1 N701 KS88P8432N-XXX function:Microcomputer

NAME PI

N

VT 1 Tuning Voltage Output TTX RST 42

RELAY 2 Relay control output STAND BY 41 Stand-by output

Y Cb Cr 3 Component input

control

AV1 4 Input select output SCL 39 IIC clock

AV2 5 Input select output SERVICE 38

6 Not used VSS 37 GND

7 Not used IR IN 36 Remote signal input

8 Not used 35 Not used

KEY IN 9 Local key input VDD 34 Vdd 5V

10 Not used RESET 33 Reset input

LV PROTECT 11 Low Voltage protect X’TAL OUT 32 X’tal output

MUTE 12 Mute output X’TAL IN 31 X’tal input

VSS 13 GND VSS 30 GND

14 Not used OSD OUT 29

15 Not used OSD IN 28

LED1 16 Stand by LED output V SYNC 27 V. Sync input

BAND1 17 Band select output H SYNC 26 H. Sync input

BAND2 18 Band select output FAST BLANK 25 OSD Fast blank output

LED2 19 On-Timer LED output R OUT 24 OSD Red output

20 Not used G OUT 23 OSD Green output

21 Not used B OUT 22 OSD Blue output

NOTE:· · Pin No. 9: Control key input (Analog to Digital Convertor)

(Max. Limit voltage)

FUNCTION MENU TV/AV POWER V+ V- P+ P-

VOLTAGE 0 0.625 1.25 1.875 2.5 3.125 3.75

FUNCTION NAME PIN FUNCTION

SDA 40 IIC data

43

53

31

30

8

.

N301 TDA8843 Function: I

2

C bus controled PAL/NTSC one chip processor

Symbol PIN Function Symbol PIN Function

SIF IN 1 B-Y OUT 29

EXT AUDIO IN 2 R-Y OUT 30

3 B-Y IN 31

4 R-Y IN 32

PLL LOOP FILT 5 CHROMA 33

VIDEO OUT 6 X’tal 3.58 34

SCL 7 X’tal 4.43 35

SDA 8 COLOR PLL 36

BANDGAP 9 +B SUPPLY 37

S Video C IN 10 CVBS SW OUT 38

S Video Y IN 11 DIGIDEC 39

VDD 12 H OUT 40

INT CVBS IN 13 FBT PULSE 41

GND 14 PH-2 42

AUDIO OUT 15 PH-1 43

16 GND 44

EXT CVBS IN 17 E/W OUT 45

BLACK

18 Y OUT- 46

CURRENT

B-OUT 19 Y OUT+ 47

G-OUT 20 IF IN 48

R-OUT 21 IF IN 49

BEAM 22 EHT 50

R-IN 23 VSAW 51

G-IN 24 V-REF 52

B-IN 25

IF AGC 53

F BLANK 26 TUNER AGC 54

Y-IN 27 DE EMPH 55

Y OUT 28 SOUND 56

N802 TDA2009A Function : audio output

Symbol PIN Function

description

NON INV IN(1) 1 LEFT IN(NON INV) N.C.+ 7 N.C.

INV IN(1) 2 LEFT IN(INV) OUT(2) 8 RIGHT OUT

SVRR 3 SVRR +Vs- 9 POWER SUPPLY-

INV IN(2) 4 RIGHT IN(INV) OUT(1) 10 LEFT OUT

NON INV IN(2) 5 RIGHT IN(NON INV) N.C. 11 N.C.

GND 6 GND

Symbol PIN Function

description

9

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N801 TDA8354Q Function : vertical output

Symbol PIN Function description Symbol PIN Function description

Vo(guard) 1 Guard output voltage GNDA 8 Ground A

Vi(M) 2 Input measuring resistor Vo(A) 9 Output voltage A

Vi(con) 3 Input conversion resistor Vp(A) 10 Supply voltage A

Vp(B) 4 Supply voltage B Ii(neg) 11 Input power stage(negative);

includes Ii(sb) signal bias

Vo(B) 5 Output voltage B Ii(pos) 12

Input power stage (positive;

includes Ii(sb) signal bias

GNDB 6 Ground B Ii(comp) 13 Input for damping resistor

compensation current

Vflb 7 Flyback supply voltage

N503 TDA9860 Universal Sound processor

Symbol Pin Function Symbol Pi

Function

n

AV1L 1 AV1 Audio Left input AV1R 32 AV1 Audio input Right

P1 2 Not used P2 31 Not used

MAINL 3 Main Audio Left

AV2R 30 AV2 Audio input Right

input

CSMO 4 Smoothing Capacitor CPS1 29 Pseudo stereo Cap. 1

MAINR 5 Main Audio Right

AV2L 28 AV2 Audio input Left

input

VP 6 Power Supply CPS2 27 Pseudo stereo Cap. 2

OUT R 7 Right Output OUT L 26 Left Output

GND 8 Ground MAD 25 Not used (GND)

LINOR 9 Line Output Right LINOL 24 Line Output Left

LINIR 10 Line Input Right LINIL 23 Line Input Left

CBR1 11 Bass Cap. Right 1 CBL1 22 Bass Cap. Left 1

CBR2 12 Bass Cap. Right 2 CBL2 21 Bass Cap. Left 2

Headphone R 13 Headphone-R output Headphone L 20 Headphone-L output

CTR 14 Treble Cap. Right CTL 19 Treble Cap. Left

MAINOR 15 Main Audio out Right MAINOL 18 Main Audio out Left

SCL 16 I2C Bus clock SDA 17 I2C Bus data

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