Daewoo DV-K882SY-AN Service Manual

DAEWOO ELECTRONICS CO., LTD.

Service Manual

MODEL: DV-K882SY-AN

PAL/MESECAM/SECAM

LECTURE

STOP

MARCHE

EJECT

ENR/IMM

R.R.

AV.R.

=

✔

Caution

: In this Manual, some parts can be changed for improving, their
performance without notice in the parts list. So, if you need the
latest parts information,please refer to PPL(Parts Price List) in
Service Information Center (http://svc.dwe.co.kr).

SPECIFICATIONS

GENERAL

Power requirement : AC 230V, 50Hz
Power consumption : Typical 18W (in PB mode)
Temperature : 5°C~35°C (Operating)

–20°C~60°C

(Storage temperature)
Operating position : Horizontal only
Dimensions (WxHxD) : 360X90X337 (mm)
Weight : Approx. 5.0Kg
Format : VHS standard
Tape width : 12.65mm
Tape speed : (SP): 23.39 mm/sec

(LP): 11.70 mm/sec
Maximum recording time
with full-size cassette : (SP): 240 min. with E-240

video cassette

(LP): 480 min. with E-240

video cassette
Maximum recording time
with full-size cassette : (SP): 45 min. with EC-45

cassette

(LP): 90 min. with EC-45

cassette

VIDEO

Signal system : PAL/SECAM colour and CCIR

monochrome signals,
625 lines/50 fields

Recording system : Rotary two-head helical scan

with a slant double-azimuth

combination video head
Input : 1.0 Vp-p, 75 ohms, unbalanced
Output : 1.0 Vp-p, 75 ohms, unbalanced
Signal-to noise ratio : 45 dB (Rohde & Schwarz noise

meter) with NETTETE IMAGE

control at centre position
Horizontal resolution : 240 lines with NETTETE IMAGE

control at centre position

AUDIO

Recording system : Longitunal track

Hi-Fi, Rotary two-head helical
scan with a slant double-azith
combination Audio head.

Input : –8 dBm, (CENELEC standard),

more than 47 k-ohms,
unbalanced

Output : –6 dBm, (CENELEC standard),

less than 1 k-ohm, unbalanced
(100 k-ohms, load)

Frequency range : 100 Hz to 8,000 Hz

Hi-Fi, 20Hz to 20KHz

Signal to noise ratio : 38 dB (More than)

Hi-Fi, 60dB (More than)

Audio Distortion : Less than 3% (SP)

Hi-Fi Less than 0.5%

TUNER

Tunning system : Voltage synthesized tuner

Programmable V/S 99 CH
(Hyper band)

RF Output : UHF channel 36

(Adjustable 30~39)

TIMER

Memory programmable : 99CH
Back up time : Less than 30 minutes
Clock exactness : In accordance with the exactness

off power supply frequency
(50Hz)

ACCESSORIES

Provided Accessories : Remote control unit

RF Cable, Battery

* Design and specifications can be subjected to change

without notice.

1

• Safety Check after Servicing

Examine the area surrounding the repaired location for damage or deterioration. Observe that screws, parts and wires
have been returned to original positions. Afterwards, perform the following tests and confirm the specified values in order
to verify compliance with safety standards.

1. Insulation resistance test

Confirm the specified insulation resistance between power cord plug prongs and externally exposed parts of the set
(RF terminals, antenna terminals, video and audio input and output terminals, microphone jacks, earphone jacks, etc.) is
greater than values given in table 1 below.

2. Dielectric strength test

Confirm specified dielectric strength between power cord plug prongs and exposed accessible parts of the set (RF
terminals, antenna terminals, video and audio input and output terminals, microphone jacks, earphone jacks, etc.) is
greater than values given in table 1 below.

3. Clearance distance

When replacing primary circuit components, confirm
specified clearance distance (d), (d') between soldered
terminals, and between terminals and surrounding
metalic parts. See table below.

Table 1: Rating for selected areas

* Class II model only.
Note: This table is unofficial and for reference only. Be sure to confirm the precise values for your particular country and

locality.

4. Leakage current test

Confirm specified or lower leakage current between B (earth ground, power cord plug prongs) and externally exposed
accessible parts (RF terminals, antenna terminals, video and audio input and output terminals, microphone jacks,
earphone jacks, etc.)

Measuring Method: (Power ON)
Insert load Z between B (earth ground, power cord plug
prongs) and exposed accesible parts. Use and AC
voltmeter to measure across both terminals of load Z.
See figure2 and following table.

Table 2: Leakage current ratings for selected areas

Note: This table is unofficial and for reference only. Be sure to confirm the precise values for your particular country and

locality.

Fig. 2

AC Line Voltage Region

Insulation Dielectric Clearance

Resistance Strength Distance (d), (d')

100V Japan ≥ 1 MΩ/500 VDC 1kV AC 1 minute ≥ 3 mm

110 to 130V

USA &

– – –

900V AC 1 minute ≥ 3.2mm

Canada

* 110 to 130 V Europe ≥ 4 MΩ/500 V DC 3 kV AC 1 minute ≥ 3 mm (d)

200 to 240 V Australia ≥ 6 mm (d')

(a: Power cord)

AC Line Voltage Region

Earth Ground

Load Z Leakage Current ( i)

(B) to:

100V Japan

i≤ 1 m A rms Exposed accessible

parts

110 to 130 V USA & i≤ 0.5 m A rms Exposed accessible

parts

i≤0.7 m A peak Antenna earth
110 to 130 V Europe i≤2 m A dc terminals
200 to 240 V Australia i≤0.7 m A peak

Other terminals

i≤ 2 m A dc

Fig. 1

1k

1.5k

1.5kµF

2k

50k

d

Primary circuit terminals

Chassis

d'

a

Z

Exposed
accessible
part

AC Voltmeter
(high impedance)

Earth Ground
power cord plug prongsB

TABLE OF CONTENTS

SECTION 1. CONTROLS AND FUNCTIONS...........................................................................................................3

SECTION 2. ELECTRICAL ADJUSTMENTS

2-1. SERVO CIRCUIT ADJUSTMENT METHOD......................................................................................................................4

2-2. VIDEO CIRCUIT ADJUSTMENT METHODS.....................................................................................................................5

2-3. AUDIO CIRCUIT ADJUSTMENT METHOD.......................................................................................................................7

2-4. IF MODULE CIRCUIT ADJUSTMENT METHODS............................................................................................................8

SECTION 3. CIRCUIT OPERA TION PRINCIPLES

3-1. POWER CIRCUIT..............................................................................................................................................................10

3-2. VIDEO CIRCUIT................................................................................................................................................................12

3-3. IF CIRCUIT OPERATION..................................................................................................................................................17

3-4. AUDIO CIRCUIT OPERATION.........................................................................................................................................19

SECTION 4. TROUBLE SHOOTING FLOW CHART

4-1. POWER CIRCUIT..............................................................................................................................................................21

4-2. PIF CIRCUIT TROUBLE SHOOTING...............................................................................................................................23

4-3. LOGIC CIRCUIT................................................................................................................................................................24

4-4. SERVO-SYSCON CIRCUIT..............................................................................................................................................26

4-5. AUDIO CIRCUIT(NORMAL)..............................................................................................................................................34

4-6. AUDIO CIRCUIT(Hi-Fi)......................................................................................................................................................36

4-7. VIDEO CIRCUIT................................................................................................................................................................38

SECTION 5. WA VEFORMS ON VIDEO CIRCUIT................................................................................................47

SECTION 6. µ-COM PORT.............................................................................................................................................51

SECTION 7. VOLT AGE CHARTS..................................................................................................................................57

SECTION 8. CIRCUIT DIAGRAM

8-1. CONNECTION DIAGRAM................................................................................................................................................66

8-2. POWER CIRCUIT..............................................................................................................................................................67

8-3. LOGIC CIRCUIT................................................................................................................................................................68

8-4. MAIN CIRCUIT..................................................................................................................................................................69

8-5. VIDEO CIRCUIT................................................................................................................................................................70

8-6. HEAD AMP CIRCUIT........................................................................................................................................................71

8-7. SECAM CIRCUIT..............................................................................................................................................................72

8-8. Hi-Fi AUDIO CIRCUIT.......................................................................................................................................................73

8-9. PIF CIRCUIT......................................................................................................................................................................74

8-10. IF MODULE CIRCUIT.....................................................................................................................................................75

8-11. A/V & SCART CIRCUIT...................................................................................................................................................76

8-12. OSD CIRCUIT, PDC CIRCUIT........................................................................................................................................77

8-13. REMOCON CIRCUIT (VR-3BC).....................................................................................................................................78

SECTION 9. COMPOMENTS LOCA TION GUIDE ON PCB BOTTOM VIEW

9-1. PCB MAIN.........................................................................................................................................................................79

9-2. PCB POWER.....................................................................................................................................................................80

9-3. PCB HEAD AMP...............................................................................................................................................................80

9-4. PCB VIDEO.......................................................................................................................................................................80

9-5. PCB IF MODULE..............................................................................................................................................................81

9-6. PCB A/V & SCART............................................................................................................................................................81

9-7. PCB LOGIC I.....................................................................................................................................................................82

9-8. PCB LOGIC II ...................................................................................................................................................................82

9-9. PCB FRONT A/V...............................................................................................................................................................82

SECTION 10. DISASSEMBLY

9-1. PACKING ASS'Y...............................................................................................................................................................83

9-2. FRONT PANEL ASSEMBLY.............................................................................................................................................84

9-3. SET TOTAL ASSEMBLY ..................................................................................................................................................85

9-4. INSTRUMENT DISASSEMBLY........................................................................................................................................86

SECTION 11. ELECTRICAL P AR T LIST...................................................................................................................94

2

! POWER ON/OFF ^ PLAYBACK
@ EJECT & REWIND/REVIEW
# VIDEO INPUT * FAST FORWARD/CUE
$ AUDIO(L/R) INPUT ( STOP
% CHANNEL UP/DOWN SELECTION ) RECORD/OTR(ONE TOUCH RECORDING)

! AUX/POUR TV JACK $ TEST SIGNAL ON/OFF SWITCH
@ DECODER JACK % ANTENNA INPUT TERMINAL
# RF OUTPUT CHANNEL ADJUSTMENT SCREW ^ ANTENNA OUTPUT TERMINAL

3

AUX/POUR TV

DECODEUR

OFF

CH.H

CH.L

TEST

SORTIE

ANTENNE

ENTREE

ANTENNE

ON

!

@

#

$%^

REAR

SECTION 1. CONTROLS AND FUNCTIONS

MARCHE

EJECT

ENR/IMM

R.R.

AV.R.

LECTURE

STOP

VIDEO G –AUDIO– D

CAN

=

!&*

)(%

^

@ # $

FRONT

4

2-1. SERVO CIRCUIT ADJUSTMENT METHOD

1. PLAYBACK PHASE

• Connection Method

• Adjustment Procedure

1) Play back the test tape.(DP-2)

2) Set the oscilloscope to the CHOP mode. Connect CH1 to the SW PULSE (PT01 PIN ¤Ø).

3) Insert PATH JIG and Press “REC” button on the remote control.

4) Check the position of the V-sync from the rising edge of the SW pulse.
(Standard: 6.5H±0.5H)

SECTION 2. ELECTRICAL ADJUSTMENT

Modulator

CH-1

OSCILLOSCOPE

CH-2

PT01

TOP VIEW

PATH JIG

6

TJ392

Video PCB

Adjustment Parts Checking Point Measuring Equipment Mode Test Tape

TJ392(Video PCB)

DP-2

Check

PT01 PIN ¤Ø

Oscilloscope Play

2-2. VIDEO CIRCUIT ADJUSTMENTS METHODS

1. REC EQ ADJUSTMENT

• Connection Method

• Adjustment Procedure

1) Set the INPUT mode to LINE mode.

2) Supply the SECAM MAGENTA signal to the VIDEO IN TERMINAL.

3) Set the VCR to the STOP mode.

4) Connect the oscilloscope to TJ401 and trigger the scope with the composite sync at TJ313

5) Adjust RL491 in order to correspond with MAGENTA EDGE section

5

TJ401 TJ313 RL491

ICL01

VIDEO PCB

VIDEO SET

SECAM MAGENTA

Signal

TOP VEW

CH-1
OSCILLOSCOPE
CH-2

SIGNAL

GENERATOR

Horizontal: 10µs/div
vertical : 500mv/div

Adj. Location Checking Point Measuring Equipment Mode INPUT SIGNAL

RL491 TJ401 Signal Gen, Oscilloscope STOP

SECAM MAGENTA

signal

6

2. PB EQ ADJUSTMENT

• Connection Method

• Adjustment Procedure

1) Set the INPUT mode to LINE mode.

2) Playback the SECAM test tape (DS-1).

3) Set the VCR to PLAY mode.

4) Connect the Oscilloscope to TJ402 and trigger the scope with the composite sync at TJ313.

5) Adjust RL492 in order to correspond with MAGENTA EDGE section.

TJ402 TJ313 RL492

ICL01

CH-1
OSCILLOSCOPE
CH-2

TOP VIEW

VIDEO PCB

Adj. Location Checking Point Measuring Equipment Mode Test Tape

R492 TJ402 Signal Gen, Oscilloscope PLAY DS-1

Horizontal: 10µs/div
vertical : 100mv/div

7

2-3. AUDIO CIRCUIT ADJUSTMENT METHOD

1. AUDIO RECORD BIAS

• Connection Method

• Adjustment Procedure

1) Set the INPUT mode to LINE mode.

2) Set the input to open mode

3) Connect the Audio level meter to both (+) and (–)

4) After inserting a blank tape, record in SP mode.

5) Adjust R292 to obtain 3.0 mVrms.

TOP VIEW

R292

3.0mVrms

+
–

A/C HEAD PCB

(+)

(–)

R01

Audio LEVEL METER

MAIN PCB

Adjustment Parts Checking Point Measuring Equipment MODE INPUT SIGNAL

R292

A/C Head PCB

Audio level meter REC No signal

R01 LANDs (+), (–)

2-4. IF MODULE CIRCUIT ADJUSTMENT METHODS

1. AFT

• AFT

IF MODULE PCB (TOP VIEW)

• Adjustment Procedure

1) Connect the attached circuit to PIN ! of P102.

2) Supply +12V to PIN# and GND to PIN @ of P101.

3) Supply +5V to PIN% and GND to PIN^ of P102.

4) Supply +5V to Pin$ and PIN^ of P101. (SECAM-L MODE)

5) Connect the signal generator output to PIN!, and GND to PIN@ of P101.

6) Connect the oscilloscope probe to check point.

7) Adjust L102 to obtain 2.5V ±0.15V DC Voltage at check point.

ADJUSTMENT PARTS

CHECK POINT TEST EQUIPMENTS INPUT SIGNAL

P102 Signal Gen. Refer to

L102 PIN! Oscilloscope the

Power Supply following.

2.5V±0.15V

R191

L101

P102

#1

#5

#2

2.2µ/50V

56K

22µ/50V

27K

15K

+12V

0.47µ/50V

10K

+5V

TEST CIRCUIT
for AFT and RF AGC
adjustment.

10K

Modulation method: 30% AM

fm: 400 Hz

fc: 38.9 MHz

Signal Level: 80 dBuV

SIGNAL GEN.

GND

OUTPUT

P101

91 91

Z102
Z103
Z101

XNO1

Z105

Q103

Q102

L103

Q105

L105

Z104

L104

ICN01

Q101

L102

Q108

Q106

LN01

<RF AGC ADJUSTMENT>

<AFT ADJUSTMENT>

OSCILLOSCOPE

CH1

#3 #5 #4 #3 #3#2 #1

#5

#3

#1

0.5mS/DIV
50mV/DIV(10:1)

"A" POINT

8

9

2. RF AGC

• RF AGC

IF MODULE PCB (TOP VIEW)

• Adjustment Procedure

1) Connect the attached circuit to PIN & of P101.

2) Supply +12V to PIN# and+5V to PIN@ of P101.

3) Supply +5V to PIN% and GND to PIN^ of P102.

4) Supply +5V to PIN$ and PIN^ of P101. (SECAM-L MODE)

5) Connect the signal generator output to PIN!, and GND to PIN@ of P101.

6) Connect the oscilloscope probe to check point("A" POINT).

7) Adjust R191 to obtain 6.0V ± 0.2V DC at the check point ("A" POINT).

6.0V±0.2V

R191

L101

P102

#1

#5

#2

2.2µ/50V

56K

22µ/50V

27K

15K

+12V

0.47µ/50V

10K

+5V

TEST CIRCUIT
for AFT and RF AGC
adjustment.

10K

Modulation method: ±30% AM

fm: 15.625 KHz

fc: 38.9 MHz

Signal Level: 92 dBuV

SIGNAL GEN.

CHI

OUTPUT

P101

91 91

Z102
Z103
Z101

XNO1

Z105

Q103

Q102

L103

Q105

L105

Z104

L104

ICN01

Q101

L102

Q108

Q106

LN01

<RF AGC ADJUSTMENT>

<AFT AGC ADJUSTMENT>

#3 #5 #4 #3 #3#2 #1

#3

#1

OSCILLOSCOPE

CH 1

0.5mS/DIV
50mV/DIV(10:1)

"A" POINT

ADJUSTMENT PARTS

CHECK POINT TEST EQUIPMENTS INPUT SIGNAL

Signal Gen. Refer to

R191 "A" POINT Oscilloscope the

Power Supply following.

3-1. POWER CIRCUIT

1. OUT LINE

The part that supply DC VOLTAGE to each circuit change AC input voltage into DC voltage. It is based on SMPS(switching
mode power supply)system which is located on main pcb. SMPS module is composed of the switching circuit and the
transformer of the primary part and the rectifier circuit of the secondary part.

2. NAME AND OPERATION OF PINS ON SMPS MODULE

1)primary part

2)secondary part

3. START UP AND NORMAL STATUS

The system of capacitor start-up is applied to DC part. As short circuit status is completed, Ib of(R803+R804/R805). Vin DC
which flows is Q801 BASE turn on Q801. The collector current, generated after Q801 trurn on, keeps the energy
W=1/2LpI*I*Ton in NP winding.
Input DC voltage is connected to both ends of NP winding.
Nb winding, m which is winded the same as NP has voltage(Vnb=NB/NP

*VinDC)and if supplies Q801with Ib through
R809,R808,807,C810 and D803 Capacitor C810 is used for speed-up of D803 which rectifies and supplies only positive
voltage left on Nb winding, to the base of Q801. At the same time C813 is charged through R810 and DZ801.

10

SECTION 3. CIRCUIT OPERATION PRINCIPLES

PIN NO NAME FUNCTION

1

AC INPUT SUPPLY AC INPUT VOLTAGE

2

PIN NO NAME FUNCTION

1 +38V

TUNING VOLTAGE OF

TUNER(33V)

2 (F+4.5V)

F/L DISPLAY FILAMENT

VOLTAGE SUPPLY

3 (F-4.5V)

F/L DISPLAY FILAMENT

VOLTAGE SUPPLY

4 -28V

F/L DISPLAY DRIVE VOLTAGE

SUPPLY
5 GND SECONDARY GND
6 GND SECONDARY GND
7 GND SECONDARY GND
8 5.8V EVER 5V, ON/OFF 5V

9 12.7V

CAP MOT, DRUM MOT(12V)

LOADING MOT(12V)

When the voltage of C813 reaches Vbe(0.7V) of Q802, Q802 is on and Q801 is off. The on-time of Q801 depends on the
time constant R810, DZ801 and C813. When Q801 is off, the energy stored on LP of primary is output through a rectifying
diode of secondary part. Then, when the core energy is used up, the diode is switched off but some energy is left in Ns
winding.
The left energy which cause the voltage in Nb winding, repeats the switching operation to turn on Q801.

4. SOFT START

A soft start circuit, as the name implies, starts to the power supply in a smooth fashion, reducing the inrush courrent
exhibited by all switching power supplies.
When the power supply is start up, Ic current is flowing in Q801 and C813 is charged from 0V.

5. CONTROL OF RATED VOLTAGE

The SMPS applies VCR controlled by detecting voltage fluctuation of 5.8V output. Generally, IC of MICOM uses 5V Vc
which has a low fluctuation.
Rated voltage is adjusted by detecting the voltage fluctuation of 5.8V, changing charge time of C813 and controlling the
switching time of Q801. IC802 consists of an OP-AMP and a zener diode which has a reference voltage(Vref).
If the output voltage is lower than 5.8V, the charge time of C813 becomes longer.
On the core of the voltage output being over 5.8V because(-) is higher than Vref Output of OP-AMP.
These changes are fed back to the primary side via the photo coupler to the switching control circuit.
As a result of it, Q801 ON/OFF frequency is changed, changing charge time of C813 to contain the constant out put
Voltage.

6. FOLD BACK CHARACTERISTICS

The most rudimentary form of fold back is like the shape shown below figure. As the load gets bigger, the on-time of Q801
becomes longer so as to supply energy; however, the on-time of Q801 in determined by the serial equivalent resistor time
constant of C813,R810,DZ801.
The on time cannot pass this time constant. So if the load requires more on-time, It does not get and output voltage of Np
winding, so the off time of Q801 becomes longer and the next on time a Q801 becomes shorter.
Ic(collector current) is reduced and output voltage goes down.

7. SNUBBER CIRCUIT

The circuit protects Q801 from surge voltage generated when the switching transistor turns off it is also required to prevent
noise.
Snubber circuit operates when Q801 is in off. the surge voltage is rectified on D802, smoothed on C808 and then the
energy is dissipated as heat on R806.

11

+

+

C807

Q801

Nb

Np Ns

Vo

Io

Vo: Secondary output voltage
Io: Secondary output current

12

3-2. Video Circuit (The operating principle of video circuit)

1. Signal flow of the luminance system in the REC mode.

The recording Video Signal (composite video signal) is input to the AGC amplifier through Pin 12 of IC301, and the sync
signal level is kept constant.
The video AGC circuit is used to keep the amplitude of video signal constant, and two types of AGCs such as "SYNC
AGC+PEAK AGC" are incorporated. The switching point for changing from SYNC. AGC to PEAK AGC is set at 110% white
level of the input video signal. The video level at Pin 4 of IC301 becomes 0.5Vp-p when a standard video signal (1Vp-p) is
applied to Pin 12 of IC301.
The signal from the AGC circuit is input to the Video AMP circuit through the QV/QH circuit. This Video AMP circuit amplifies
input video signal by about 6dB, and then is input to the buffer (composed of Q309 and R323) through Pin 16 of IC301.
The other signal is as follows:
The chrominance component in the AGC circuit is filtered by a LPF (Low Pass Filter) and the luminance signal (eliminated
chrominance) is fed to the YNR circuit.
In the circuit, vertical enhancing is used for the luminance signal, using an external 1H Delayline (CCD IC: LC89970), and it's
output is fed to Pin 4 of IC301. The output signal from Pin 4 of IC301 is input to Pin 5 through the subemphasis circuit. This
signal is then fed to emphasis circuit (consists of Detail Enhancer, Non-linear Emphasis and MAIN Emphasis). Then its high
frequencies of the output signal are enhanced by this Emphasis circuit.
This signal is fed to the FM Modulator, and the recording Y-FM signal is obtained from Pin 2 of IC301.
This signal is input to the PREAMP IC (Pin 8 of LA7411: 2 Head, Pin 11 of LA7416: 4 Head).

Video

AGC

QV/QH

Video

AMP

LPF YNR

Sub-

emphasis

buffer

CLAMP

IH DELAY CCD

IC302

REC

EQ

FM

MOD

MAIN

EMPHA

NL

EMPHA

CARRIER

SHIFT

To. PREAMP CIRCUIT
LA7411 * PIN INPUT
LA7416 1 PIN INPUT

Video input

2 6

buffer

To OSD

$ %

*^

80

@

*&^

BLOCK1. Luminance signal flow in the record mode.

fsc : 4.433619MHz

13

2. Signal flow of the PAL colour in the record mode

A recording composite video signal is fed to the AGC circuit from Pin 12 of IC301, and its output signal is passed through a
BPF (Band Pass Filter) to eliminate the luminance components, and then only the colour signal is fed to the ACC (Auto
Colour Controller) amplifier. The gain of the ACC amplifier is controlled by the DC voltage at Pin 41 of IC301.
The signal from ACC AMP is fed to the Main Converter to transfer 4.43MHz to 627KHz. That is, the summation and
substraction of the two input signal frequencies are obtained from this Main Converter. Here, the two input signal
frequencies are 4.43MHz and 5.06MHz. The output frequencies from the Main Converter are approximately 627KHz and

9.49MHz. The output from the Main Converter is fed to the killer circuit through the LPF. The LPF is used to eliminate
unwanted frequencies (ie: 9.49MHz).
The Killer detector gives a reliable operation thanks to the application of both systems i.e. synchronized detection (APC
Killer) and the Peak detection (ACC Killer) in the record mode. The signal is obtained from Pin 38 of IC301 as the recording
colour signal. The output signal from Pin 38 of IC301 is fed to the PREAMP IC (2 Head: Pin 7 of LA7411, 4 Head: Pin 10 of
LA7416).

3. Signal flow of the luminance in the playback mode

The play-back Y-FM from the PREAMP (approximately 60dB amplification) is fed to the PB EQ circuit to perform frequency­limiting and phase compensation. The output signal from the PB EQ circuit is input to Pin 1 of IC301 and then this signal is
passed through the FM-AGC so that the signal level is kept constant. The output signal is fed to a Double Limiter. The
Double Limiter's function is as follows:
As the high frequency components of the play-back Y-FM signal are deteriorated due to the characteristics of the Tape­Head system, Y-FM signal (black spike) effect in the play-back picture, and the Double Limited is used to compensate for
this.
The signal from the Double Limiter is fed to an FM Demodulator. This demodulated video signal is passed through the LPF
and the emphasizied high frequency component from the Main Emphasis is de-emphasized. The signal from the Main DE­emphasis is fed to pin 4 of IC301.

Video input

2

Video

AGC

BPF

ACC
AMP

MAIN

CONV

IMHz

LPF

Killer

4.43MHz 4.43MHz

(5.06±4.43)

MHz

5.06MHz

O

u

I

To. PREAMP
2Head: Pin & of LA7411
4Head: Pin ) of LA7416

BLOCK 2. PAL COLOR SIGNAL FLOW

627KHz

14

This signal from Pin 4 of IC301 is then passed through a sub-deemphasis and Buffer and fed to Pin 5 of IC301.
The signal input to Pin 5 of IC301 is fed to the YNR through a LPF. The YNR circuit gives considerable noise reduction
affects. The signal from the YNR circuit is fed to the Y/C Mixer circuit through the Non-linear Deemphasis, the Double High
Pass Noise Canceller (DHPC), and the Picture Controller circuit. The signal is then mixed with the playback colour signal
and the PB Video Signal is obtained from Pin 16 of IC301 through Quasi-Vertical/Quasi-Horizontal (QV/QH) Insertion circuit
and the Video Output Amplifier (about 6dB amplification). The output of Pin 16 (approximately 2Vp-p) is input to the Buffer
circuit (consists of Q309 and R323).

4. Signal flow of the PAL colour in the playback mode

FM

AGC

Double
Limiter

FM

Demod

L P F

Main

De-empha

L P F

Sub-deempha

& buffer

Y N R

N L

De-empha

Double HP

Noise Can

Picture

Controller

IH Delay

CCD

IC302

Video

AMP

QV/QH

Y/C
MIX

R322

R323

Q309

TO OSD CIRCUIT

6

$

%

%0*

8

!

Y-FM input

BLOCK 3. PLAYBACK LUMINANCE SIGNAL FLOW

Butter

1.3MHz
LPF

PB color input

u

ACC
AMP

Main

Conv

4.43MHz
BPF

627KHz 627KHz

5.06MHz

± 627KHz

NAP

PB AMP

/Killer

2H Delay

IC302

Y/C

Mixer

+=

$
@

“

q

E

w

From. PB luminance

signal

5.06MHz

fsc (4.433619MHz)

PB SECAM

Colour input

BLOCK 4. PB PAL COLOUR SIGNAL FLOW

4.43MHz

4.43MHz

IC303

!

)

PAL : LOW

MESECAM : HIGH

15

The signal from the PREAMP circuit is fed to Pin 38 of IC301 and then this signal is amplified by 60dB (almost 1000 times).
The signal from Pin 38 of IC301 is filtered by the LPF. That is, the LPF is used to eliminate the luminance signal. The down­converted colour signal (627KHz) from the LPF is fed to the Main Converter through the ACC amplifier circuit. The output
from the Main Converter is fed to Pin 23 and 24 of IC301 through a BPF (4.43MHz). The colour signal frequency of Pin 24 of
IC301 is 4.433619MHz. The output signal at Pin 24 of IC301 (LA7437) is input to Pin 1 of IC303 (LA7356: SECAM
DETECTOR) in order to detect whether the colour signal is PAL or MESECAM. After filter out the crosstalk components by
an external CCD IC (LC89970), this signal is input to Pin 26 of IC301. The output of Pin 26 is fed to Pin 29 of IC301 through
a PB AMP/Killer and NAP circuit. The colour signal from Pin 29 is fed to the Y/C Mixer through Pin 28.

5. Signal flow of the SECAM colour in the record mode

The video signal is input to a 4.3MHz BPF through Pin 1 of ICL01 (BA7207S: SECAM colour). The signal at Pin 1 is fed to
the REC BELL circuit to be de-emphasized.
The REC BELL output is then fed to Pin 26 of ICL01.
This signal is input to Pin 1 of ICL02 (LA7356: SECAM DETECTOR) and Pin 24 of ICL01 (BA7207S)
The signal input to Pin 1 of ICL02 is used to detect whether the signal is SECAM or non-SECAM. If this signal is the SECAM
colour, the voltage at Pin 10 of ICL02 is high (almost 4.0 volts). If not, the voltage at Pin 10 of ICL02 is low.
The other signal from Pin 26 of ICL01 is fed to Pin 24 of ICL01 through the 12dB AMP circuit (consists of RL425, RL426,
RL427, RL428, RL429, CL429 and QL413). The signal from Pin 24 is fed to the Limiter. In this Limiter circuit, the output
amplitude is limited. The Limiter output is fed to a 1/4 divider circuit in order for the colour signal to be divided by 4. This
signal is then fed to the REC SYNC GATE circuit. The noise of the SYNC part is removed by the REC SYNC GATE. The
REC SYNC GATE output is fed to the 1.1MHz BPF so that the unwanted signal can be eliminated. The 1.1MHz BPF output
is fed to Pin 28 of ICL01 through the REC EQ circuit.

4.3 MHz
BPF

REC

CELL

Main

De-empha

1/4 Divider

Limiter

12dB

AMP

q!

PB color input

=

REC

SYNC GATE

1.1 MHz
BPF

REC

EQ

=

REC SECAM

BLOCK 5. RECORD SECAM COLOUR SIGNAL FLOW

16

6. Signal flow of the SECAM colour in the playback mode

The output signal (mixed the luminance and colour) from head is input to the PREAMP IC. This signal is amplified by about
60dB (approximately 1000 times) by the preamp IC. The signal from the PREAMP IC is fed to 1.1MHz BPF circuit (consists
of CL421, RL410, LL408, CL408 and RL411). The luminance signal is eliminated by the 1.1MHz BPF circuit. This output
signal is fed to Pin 18 of ICL01. The output at Pin 18 is input to a 1.1MHz BPF and the unwanted signal is eliminated. The
signal from 1.1MHz BPF circuit is input to the PB EQ circuit. This signal is flattened by this circuit. The flattened signal is
then input to the Limiter circuit. In this circuit, the signal is limited. The limited signal is fed to the X2 circuit to give the signal
with double frequency. The doubled frequency signal output is fed to a 2.2MHz BPF circuit to eliminate the unwanted
signal, and then is input to another X2 circuit. Therefore the new signal has a quandrupled frequency. After the quadrupled
signal is input to a 4.3MHz BPF in order to eliminate the unwanted signal, it is fed to Pin 26 of ICL01. The output signal at
Pin 26 is input to Pin 1 of ICL02 and the 12dB AMP circuit. The signal input to Pin 1 of ICL02 is used to detect whether the
signal is SECAM or non-SECAM. The other signal is input to the 12dB AMP circuit. The 12dB AMP output signal is fed to
the Limiter circuit through Pin 24 of ICL01.
In the Limiter circuit, the amplitude of the signal may be limited. The signal from the Limited circuit is input to the PB SYNC
GATE circuit to eliminate a noise from the SYNC part, and then fed to Pin 6 of ICL01 through the 4.3MHz BPF and the PB
BELL circuit. The signal from Pin 6 is input to Pin 8 through a 2.1MHz Trap to remove the spurious components. The signal
at Pin 8 is fed to Pin 11 of ICL01 through 6dB AMP circuit.
The signal at Pin 11 is input to Pin 29 of IC301 (LA7437: Y/C IC).

PB

AMP

PB Color

from PREAMP

1.1MHz
BPF

1.1MHz
BPF

PB

EQ

X2

2.2MHz
BPF

X2

Limiter

4.3MHz
BPF

12dB

AMP

Limiter

PB

SYNC GATE

6dB

AMP

ICL02

SECAM

DETECTOR

PB

BELL

4.3MHz BPF

To. pin E of IC301

1

PB SECAM

SECAM(H)

2.1MHz
Trap

4.286MHz
Trap

SECAM:HIGH

non-SECAM: LOW

8

=q

!

)

*^

BLOCK 6. PB SECAM COLOUR SIGNAL FLOW

17

3-3. IF CIRCUIT OPERA TION

1. VIDEO SIGNAL FLOW

The signal from the ANT is amplified for selectivity, to decrease image interference, and increase S/N using the RF AMP.
The RF signal at the MIXER is subtracted from the LOCAL OSC frequency using the upperside band method, to change it
into the IF signal; 38.9MHz. The IF signal converted from the RF signal in the tuner block amplified by about 30dB to
increase S/N in the pre-amp block. The reason for this is that the SAW filter has its own insertion loss of about –18 to
–22dB. The SAW filter is a kind of BPF, used to remove the near channel harmonics and make the desired frequency
response. The IF AMP desired of about 60 to 70dB gain for receiver sensitivity and selectivity. The vision IF AMP consists
of three AC-coupled differential amplifier stages; each stage uses a controlled feedback network called AGC. To maintain
the video output signal at a constant level the automatic control voltage is generated according to the transmission
standard. For negative modulation in the PAL standard the peak-sync level is detected, and for positive modulation in the
SECAM standard the peak-white level is detected. The AGC detector charges and discharges the AGC capacitor to set
the IF gain and the tuner gain. The standard is switched by the µ-COM. We can also adjust the tuner AGC voltage take
over point. This allows the tuner and the IF SAW filter to be matched to achieve the optimum IF input signal. The IF
amplifier output signal is fed to a frequency detector and to a phase detector. The frequency detector is operational before
lock-in. A DC current is generated which is proportional to the frequency difference between the input signal and the VCO
frequency. The control voltage for the VCO is provided by the phase detector.
The video modulator is a type of the multiplier. The vision IF input signal is multiplied by the in-phase component of the
VCO output. The demodulated output signal is fed via an integrated LPF (about 12MHz) to the video amplifier for
suppression of the carrier harmonics.
The polarity of the video signal is switched in the demodulated stage according to the standard switch. The VCO operates
with a symetrically-connected reference L-C circuit, running at the double vision carrier frequency (77.8MHz) to decrease
the frequency error. Frequency control is performed by an internal varicap diode. The voltage used to set the VCO
frequency to the actual double vision carrier frequency, is also amplified and converted to give the AFC output current.
The AFC output is fed to the tuner to change the LOCAL OSC frequency and to the µ-COM for channel searching. The
VCO signal is divided by-two in a travelling wave divider, which generates two differential output signals with exactly 90
degrees phase difference, independant of frequency. The video signal passing through the 5.5MHz sound trap is fed to
the buffer.

2. PAL AUDIO FLOW

The FM sound intercarrier signal passing through the 5.5MHz sound BPF is fed to a limiter amplifier before it is
demodulated.
This gives high sensitivity and AM suppression. The limiter amplifier consists of seven internal AC-coupled stages,
minimizing the DC offset.
The FM-PLL demodulator consists of an RC-oscillator, loop filter and phase detector. The oscillator frequency is locked
on to the FM intercarrier signal from the limiter amplifier. As a result of this locking, the RC-oscillator is frequency
modulated. The modulating signal voltage is used to control the oscillator frequency using this technique, the FM-PLL
works as a FM demodulator. The AF signal coming out of the FM-PLL demodulator is amplified and buffered in an output
stage.

RF

AMP

MIXER

PRE-

AMP

SAW

FILTER

IF

AMP

VIDEO

DET &

DE MOD

SOUND

TRAP

BUFFER

VIDEO

OUT

VCO AFC

AGC
DET

LOCAL

OSC

µ-COM

STANDARD S/W

TUNER

ANT

VIDEO DET

& DEMOD

SOUND

BPF

intercarrier

VIDEO BLOCK

LIMITER

AMP

FM PLL-

DEMODE

AF

AMP

AUDIO OUT

18

3. SECAM AUDIO FLOW

Because the SECAM TV sound system uses amplitude modulation, we need an AM-sound demodulation process. The
sound IF signal passing through the SAW filter is fed to the sound IF amplifier which consists of three AC-coupled
differential amplifier stages each with about 20dB gain.
At the output of each stage is a multiplier for gain controlling. The automatic gain control voltage, used to maintain the AM
demodulator output signal at a constant level, is generated by a mean level detector. This AGC detector charges and
discharges the AGC capacitor controlled by the output signal of the AM demodulator which is compared to an internal
reference voltage.
The IF amplifier output signal is fed to a limiting amplifier.
The limiter output signal (which is no longer AM modulated) is also fed to the multiplier. In this way we get AM
demodulation (in phase demodulation).
After lowpass filtering (400KHz) for carrier rejection and buffering, the demodulator output signal is fed to an operational
amplifier with three input stages and 0dB gain. One input is SECAM sound, the other is PAL sound. A sound mute control
signal can also be used to mute the OP amplifier output.

4. DIGITAL AUDIO FLOW

The demodulator function includes integrated baseband filters for pulse shaping and unwanted signal rejection, automatic
gain control, a low jitter integrated VCO.
the decoder function performs the descrambling, de-interleaving and reformatting operations required to recover the
original data words.
The data words are processed through a stereo digital filter, digital de-emphasis network, second order noise shaper, and
256 times over sampling bitstream audio DAC.
The whole device supported by 8.192MHX crystal oscillator, and I

2

C serial data bus for communications with µ-com.
In the output stage out selector can automute the nicam signal to normal audio when the digital data have noise more
than error rate.
It also can be switched manually by user.

PRE-

AMP

SAW

FILTER

IF

AMP

AM

DE MOD

O db

LIMITER

AMP

L/L' control PAL SOUND

Standard S/W

AUDIO OUT

mute

BASE BAND

FILTER

&

AGC GAIN

STAGE

PHASE DETECT

&

DATA

SLICERS

NICAM728

DECODER &

DEVICE

CONTROLLER

DIGITAL

FILTER

&

NOISE

SHAPER

BITSTREAM

DAC

OUT S/W

&

BUFFER

OUT.L

OUT.R

DQPSK

I C DATA X-TAL NORMAL AUDIO

DECODERDEMODULATOR

2

3-4. AUDIO CIRCUIT OPERA TION

1. Signal flow of Normal audio in REC mode.

The recording audio signals from IF circuit are input to the inputselector through pin 2 (left), 3 (right) of the IC201 and the
input signal are selected.
This audio AMP circuit amplifies input audio signal by about 4DB and then the signals are mixed. The AGC circuit is used
to keep the amplitude of audio signal constant. The signal from the AGC circuit is input to the REC EQ circuit through
buffer. This REC EQ circuit amplifies input audio signal by about 12DB. This signal from REC EQ circuit outputs to the pin
33 of IC201, and then the signal is recorded on tape with external AC bias to the audio head.

2. Signal flow of Normal audio in PB mode.

The audio signal from audio head to pin 34 of IC201 is fed to the PB EQ circuit.
Time constant of PB EQ circuit is controlled by I2C BUS with control byte.
Output selector circuit separates the audio signal from mute circuit into two audio signals and then the audio signals
output to pin 21 (left) and pin 22 (right) separately.
we designed that the amplitude of the output signals is –6dBm.

19

Input Selector

Volume L

Audio

AGC

@
#

Volume R

+

E

REC

EQ

T

WeR

Audio input

LEFT

RIGHT

AMP 4dB

To A.HEAD

Buffer

t

PB
EQ

yY

A.MUTE

Output

Selector

Line

Selector

“

‘

LP

Buffer

LEFT

RIGHT

Audio Output

LEFT

RIGHT

Audio input

BLOCK A-1. Normal audio signal flow in the REC mode.

BLOCK A-2. Normal audio signal flow in the PB mode.

3. Signal flow of Hi-Fi audio in REC mode.

Input signals from IF circuit are selected in inputselector and then the signals are amplituded by 4dB in AMP circuit.
Audio signal at the input passes the audio low-pass filter and noise reduction system. The audio signal at the output is not
processed by the noise reduction and can be used to monitor the recording. The noise reduction executes a combination
of pre-emphasis and dynamic compression on the signal. Thereafter the audio signal is fed to an audio clipper and is then
FM modulated in the modem. (Modulator & Demodulator circuit)
Carrier frequencies used are 1.4MHz for the left-and 1,8MHz for the right audio channel in PAL mode. The modulated FM
carrier is then lowpass filtered in the HF lowpass filter and the carriers of both channels are added together. The carriers
are now available at pin 56 FMOUT and fed to the Hi-Fi preamp IC (input of BA7746FS pin 10)

4. Signal flow of Hi-Fi audio in PB mode.

The two audio carrier read from tape are input at pin 51 FMIN. The signal is now routed via the HF AGC to the integrated
bandpass filters. Each bandpass filter then passes the carrier of interest to the HF limiter and modem. The amplitude of
the signal at the output of the bandpass filter is measured in the level detector. The level detector signal of both channels
is combined and fed back to the AGC. This way large carrier signals are attenuated avoiding saturation of the bandpass
filters. The modem, switched as a PLL, now demodulates the FM carrier. The audio output signal of the modem is then
going through the S & H, which suppresses the so called 'headswtich noise' and audio disturbances caused by tape
drop-outs. Hereafter the signal passes the audio lowpass filter, removing high frequency noise, and the original signals is
reconstructed by dynamic expansion and de-emphasis in the Noise Reduction circuit. Noise Reduction processing in
Playback is exact complementary to that used in Record mode. If the left channel carrier at FMIN falls below the mute
level of 4.2mV (RMS value) the audio signal is mute in front of the lowpass filter. If the FM signal has been mute the output
selection will automatically switch to NORMAL mode. The audio signal from Noise Reduction circuit passed Audio FM
Mute circuit and then Output selector and Line selector select the output audio signals to pin 21 and pin 22 of IC201.

20

Input Selector

Volume L

@

#

Volume R

A.LPF

A.LPF

N.R.

N.R.

audio

clipper

audio

clipper

modem

1.4MHz

modem

1.8MHz

H

D

1.4MHz
HPF

1.8MHz
HPF

+

A.MUTE

f

Buffer

Audio input AMP 4dB

To. PREAMP circuit
(BA7746FS

) pin input)

LEFT

RIGHT

HF AGC

BPF

G

Audio input

BPF

HF

limiter

level

detect

HF

limiter

level

detect

modem

1.4MHz

modem

1.8MHz

D

S&H

S&H

Audio

LPF

Audio

LPF

DOC

MUTE

j

DOC

Noise

Reduction

Noise

Reduction

A.FM

Mute

A.FM

Mute

Output

Selector

Line

Selector

LEFT

RIGHT

“

‘

LEFT

RIGHT

Audio Output

H

BLOCK A-3. Hi-Fi audio signal flow in the REC mode.

BLOCK A-4. Hi-Fi audio signal flow in the PB mode.

21

SECTION 4. TROUBLE SHOOTING FLOW CHART

4-1. POWER CIRCUIT

When changing the parts which are broken first, remove the power plug from the socket and then discharge the voltage
across the terminals of C807 (use an external KΩ resistance).
When check the primary circuit, Use the oscilloscope isolated properly (Use the isolated transformer) and connect GND to
the primary GND, however It is not necessary to isolate the oscilloscope when check the secondary circuit.

No output Voltage.

Prepare the oscilloscope connected

the isolated transformer

YES

Check F801 Fuse.

YES

Is voltage applied to D801?

YES

Is voltage applied to the

terminals of C807?

YES

Is voltage applied to the Q801 base?

YES

Is voltage output from pin # of

IC801?

YES

Check R806, D802, R807,

R808, R809, DZ801

YES

Check the Secondary circuit

YES

Check L801, L802

Check R802, D801

Check R803, R804, R805, C811

Check Q802

YES

NO

NO

NO

YES

A. CHECKING THE PRIMARY CIRCUIT.

22

Check DZ802

Check each output voltage

YES

Check the P802

YES

END

Check transformer of NO

output stages

B. CHECKING THE SECONDARY CIRCUIT.

YES

Check the COIL,C of NO

output stages

NO

Check the diode of NO

output stages

YES

23

4-2. PIF CIRCUIT TROUBLE SHOOTING

RF output signal N.G

Is video signal output

from P101 * pin?

Is video signal input

into P101 * pin?

YES

Is +2.5V supplied

at P101 & pin?

YES

Is +6V output from

P101 & pin?

YES

Check R180

R181, R153

YES

A/V sw module

P153 % pin?

Check US pin

tuner-modulator

YES

Is audio signal output

from P102 @ pin?

NO

Check QL01

RL12, RL18

NO

Check A/V

sw circuit

YES

YES

NO

Is tuner voltage

supplied?

(+12V, 32V)

US pin

re-connect

NO

Change IF

module

NO

Check Q157
Q158, Q159

Check IC601

pin126

Check power

circuit

YESNO

Is BAND

SELECTION/Data

supplied at IC601

37, 39, 40 pin?

YESNO

Change

tuner

Check timer

cirucit

YES

NO

YES

24

4-3. LOGIC CIRCUIT

Digitron does

not operate.

Is +5V supplied to

pin of IC701?

8

Is -24V supplied to

pin of IC701?

11

Are -20 and -16.5V

supplied to pin and

of G701?

1

35

Are CLK signals

supplied to pin ), I

and i of IC701?

Is 5V at pin of

IC701?

7

Check X701

Check IC701

and change.

Check power circuit

Is +5.8V supplied

from D713 cathod

Is -24V at D607

anode?

Check D806 and

primary power circuit.

Check the connector

and pattern.

Check the power

module

Check IC601

Change

Change

YES

YES

YES

YES

YES

YES

NO

NO

NO

NO

NO

NO

NO

NO

YES

A.

25

Digitron is lit keys do

not operate.

Is each key pulse

applied to pin ,

and of IC701?

2 3

12 13

Check key matrix

circuit.

Check the pin serial of
pin , ~ of IC701.

19 22 24

NO

YES

B.

26

4-4. SERVO-SYSCON CIRCUIT

PLAYback picture

is not good

Noise apperars although

adjusting tracking.

Noise shakes up and
down on the screen?

YES

Adjust tracking.

NO

A.

Is CTL pulse output

at pin ‹ of IC601?

YES

Is CTL pluse input to

pin ⁄, ¤ of IC601?

YES

The voltage of pin

of IC601 is not changing?

YES

Check IC601.

YES

NO

Noise appears

although change

cassette tape.

NO

Check C510, C511.

NO

Check R504, C505.

NO

Check and re-adjust

the path of Deck.

YES

CTL HEAD height

is normal and

there is not dust?

Adjust the HEAD

height and

remove dust.

YES

Check circuit

adjacent to IC601.

NO

118

27

Playback picture

is not good.

Noise appears on the

screen on the whole.

Are SW-pulse and HA-SW
applied to preamp circuit?

YES

B.

Is Enve. waveform

supplied to pin $ of

PT01?

YES

Check video circuit.

YES

NO

Is sw pulse supplied

from pin 9 of IC601?

Check D. PG input

and connector.

YES

Check pattern

NO

NO

Check connector,

Head Amp

and Head dust.

Changed Head.

NO

NO

Noise appears on the

screen at the bottom

Check flow A.

YES

Connect the pin

of IC601 to GND for

a few of seconds.

NO

117

28

Auto-stop during

playback.

Is reel pulse applied to

pin $ and % of IC601?

Is D. FG applied to

pin > of IC601?

YES

C.

Check IC601.

YES

NO

Check connector and

D. FG circuits.

NO

Check reel sensor.