Viewsonic a90fplus-1 Service Manual

Service Manual

ViewSonic A90f+-1

Model No. VCDTS23307-2R

19” Digital Controlled Color Monitor

ViewSonic

(A90f+-1_SM_602-Rev. 1.0-October 2002)



381 Brea Canyon Road, Walnut, California 91789 USA - [phone]

Copyright

Copyright
reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language or
computer language, in any form or by any means, electronic, mechanical, magnetic, optical, chemical,
manual or otherwise, without the prior written permission of ViewSonic Corporation.

Disclaimer

ViewSonic makes no representations or warranties, either expressed or implied, with respect to the
contents hereof and specifically disclaims any warranty of merchantability or fitness for any particular
purpose. Further, ViewSonic reserves the right to revise this publication and to make changes from time
to time in the contents hereof without obligation of ViewSonic to notify any person of such revision or
changes.

Trademarks

ViewSonic is a registered trademark of ViewSonic Corporation.
All other trademarks used within this document are the property of their respective owners.

2002 by ViewSonic Corporation. All rights reserved. No part of this publication may be

¤

Revision History

Revision Date Description Of Changes Approval

1a 10/9/02 Initial Release DCN-2658 K.Yang
1b 11/05/02 Revise DCN-2658 C.Shen

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TABLE OF CONTENTS

1. Precautions and notices ......................................................1

2. Specification.......................................................................3

3. Control Location and Functions ........................................5

4. Disassembly instructions ...................................................9

5. General Connections & applications ...............................11

6. Electronic Circuit Description .........................................13

7. Adjustment ......................................................................19

8. Troubleshooting Flow Chart.............................................28

9. Recommended Spare Parts List........................................35

10. Electrical Parts List.........................................................37

11. Block Diagram................................................................53

12. PCB Layout.....................................................................54

13. Schematic Diagram.........................................................57

14. Exploded Diagram.......................................................... 64

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1. Precautions and Notices

1.1

SAFETY PRECAUTIONS

1) Observe all cautions and safety related notes located inside the display cabinet and on the display
chassis.

2)Operation of this display outside the cabinet or with the cover removed, may involves a shock harzard
from the display power supplies. Work on the display should not be attempted by anyone who is not
thoroughly familiar with precautions necessary when working on high voltage equipement.

3)Do not install, remove or handle the picture tube in any manner unless shatter-proof goggles are worn.
People not so equiped should be kept away while handling picture tube. Keep picture tube away from
body while handling.

1.2 Observe all cautionary and safety related notes located on the chassis, cabinet and display tube.

1.3 Operation of the monitor with the back cover removed presents a potential shock hazard. Only

personnel familiar with the precautions necessary for safe working on high voltage equipment should
attempt to carry out servicing.

1.4 Always wear shatter proof goggles when removing, installing or generally handing the picture tube.

People not so equipped should be kept at a safe distance when any such handing is being undertaken.
Do not handle the picture tube by the neck of deflection coil. Do not carry the picture tube resting against
the body.

1.5 The picture tube is designed and constructed to limit X-Radiation to a safe level during normal operation.

To maintain the required level of protection and safe operation, replacement tubes must be correctly
adjusted and any protective circuits must not defeated.

1.6

IMPORTANT-Safety Tests

After servicing, and before returning the monitor to the user, a thorough safety test must be carried out
to ensure there is no potential shock hazard to any operator(s) using the monitor.
All the following test must be performed. A monitor failing any of these tests should be rejected and have
the problem rectified.

1.7

A.C. Leakage Test

Remove the power sourse. Connent the monitor to the circuit as in figure 1 below. Switch the monitor
on/off switch to on. A reading of less than 3.5mA should obtained (ref. EN60950).

Equipment
Under test

Isolating
transformer

L

N

Equipment safety

Measuring instrument

Fig. 1 Measurement of AC Leakage Current

Earth terminal

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1.8 Voltage Breakdown Test

Connent the live pin and neutral pin together. Switch the monitor on/off switch to on. Apply 1500VAC
RMS or 2250VDC, 50Hz for one minute between this connection point(live and neutral pin short) and
earth. Ensure no voltage breakdown occurs.

1.9 Earth Resistance/Continuity Test

Measure the resistance between the signal cable metal shell and the earth pin in the A.C. socket. At a
current of 25 amperes, the resistance should be less than 500mohm.
NOTE: A portable appliance tester (PAT) is a suitable instrument to use for the above safety tests.

1.10 H.V. Over Voltage Protection (Required for X-Radiation Safety)

Adjust R176 slowly anti-clockwise until the over voltage protection circuit is activated, and the high
voltage must be less than 33KV just before the activation. After test, R176 should be adjusted back to
normal(=25.9KV)

CAPACITOR:

C850 400V 4700PFM CAPACITOR.CERAMIC 5230105501
C851 400V 4700PFM CAPACITOR.CERAMIC 5230105501
C135 250V 33UFM CAPACITOR.ELECTROLYTIC 5214433012
C139 100V 330UFM CAPACITOR.ELECTROLYTIC 5214019612

RESISTOR

R827 1/4w 2K ohm RESISTOR.VR 5162161220

SEMICONDUCTORS

I803 UC3842N IC LINEAR 6644063111
I301 TDA9116 SDTP-32 IC.LINEAR A.S.D.C. 6644076308
I310 TDA8172 7P IC.LINEAR 6644076000
I101 UC3842N IC.LINEAR 6644063111
IA01 NT68F62U SDIP-42 IC.LSI MCU 6647008204
Q121 2SK2843 TR FET MOS 6626003202
Q433 BU4525AX TR NPN 6621002801
Q801 2SK2648 TR FET MOS. 6626003208
D827 HZ5C1 DIODE ZENER 6615007834

OTHERS

SR801 CSA-SS-212DM5 RELAY 5054613402
F801 250V/3.15A FUSE 5054431539
T801 TPW-697 POWER TRANSFORMER 5061369700
T101 (RA) TFB-280T TRAQNS.FLYBACK COLOR 5062628031
T101 (RB) TFB-280L TRAQNS.FLYBACK COLOR 5062628032

V901 (RA) M46QCK761X123 (TCO

MDT)

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CCRT/DY 5051286346

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2. Specifications

Size and deflection angle 19 inch 90 degree
Screen type Pure, Flat, High Brightness

CDT

Scanning
Freq.

Video amplifier Applicable pixel rate 175MHz
Resolution
Modes

Power

User controls

Rear

connection

Horizontal pitch / Dot pitch 0.22mm / 0.25mm
Surface treatment Anti-static AR coating
Transmission rate 52.6%
Horizontal Frequency 30kHz to 86kHz
Vertical Frequency 50Hz to 150Hz

Maximum 1600 x 1200
Factory preset/User modes 13 / 10
AC input range 100 to 240 Vac
Max. power consumption

Power Management

Power Switch On/off with Led indicator

Up/Down adjustment Key

“1” “ 2” Key
“UltraBrite Mode “Key As a select key/ go to High Bright Display mode

Signal

connections

Standard Model 1.8 m signal cable with 15Pin D shell miniature

Normal <110 W
Off <3 W

110W

2 key pads for adjust
Up / down keys are direct access for Contrast
And Brightness adjustment

As a select key/ go to next sub menu

male connector.

Power input AC socket with 1.8 meter cable

Agency
Approvals

European

USA

Plug and Play DDC 1/2 B Version 2

Operating Temperature

Environmental
Conditions

Dimensions W x H x D 575 mm x 600mm x 630mm
Weight Kg 25.5Kg (Gross)

Storage Temperature
Operating Humidity 10% to 90%
Storage Humidity 10% to 95 %

Safety CB,

Emissions EN50081-1

Immunity EN50082-1

Ergonomic

VLMF MPRII
EPA Energy Star
Safety UL1950, Cul950 or CSA 22.2
Emissions FCC class B
X-ray DHHS
Regulatory Filing VCDTS23307-XYZ

ISO9241Paart3 &ISO9241Part8

0qC to 40qC
–40qC to +60qC

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Noted that A90f + belong to MPR II models.

Alignment default conditions:

3.1 Room luminance: 225 LUX.

3.2 Warm up: Mis-convergence: 30 minutes (Full white display).
Other spec.: 20 minutes.

Display usable: 15 sec.

3.3 CDT direction : East

3.4 Pattern generator : CHROMA 2250 or equivalent.; (Video O/P: 0.7 Vpp).

3.5 Earth Magnetic field:

Northern Hemisphere: Bh : 0.25 +/- 0.01 GAUSS ; Bv : 0.45+/- 0.01 GAUSS –U03 model.
Southern Hemisphere: Bh : 0 +/- 0.01 GAUSS , Bv : -0.52 +/-0.01 GAUSS.

3.6 AC Power input: 110V AC, 50/60 Hz ;230V AC ,50 /60Hz.

3.7 Ambient temperature: 20 ² 5 ʑ.

3.8. Preset Mode Timing: Total 13 Pre-set Modes + 1 mode (mode 5 for self test setup)

MODE RESOLUTIO

N
H X V

NO.

VGA

VGA 640 X 400

MAC 640X480

VESA
85Hz

VESA
75Hz
MAC 832X 624

VESA
75Hz

VESA
85Hz

VESA
75Hz
VESA 1024 X 768

640 X 480
1

2

3

640X480
4
640 X 480
5 (for
auto-size
reference)
800 X 600
6

7
800 X 600
8
1024 X 768
9
1024 X 768
10
1024 X 768
11
1600 X 1200
12
1280 X 1024
13

14

H.FREQ
(kHz)
V.F RE Q(
Hz)

31.469

59.94

31.469

70.078

35.0

66.667

37.5

43.269

85.008

46.875

49.725

74.5

53.674

85.061

60.023

75.029

60.241

74.927

68.677

84.997

75.0

79.976

75.025

48.363

60.004

H.
POLART
Y
V.

Composit

75

75

60




-

+

e

Negative







+
+




+
+





 16.6













HORIZ.
TOTAL

USEC

31.778 25.422 1.907 3.813 16.683 15.253 1.049 0.064 25.175

31.779 25.422 1.907 3.813 14.269 12.712 1.112 0.064 25.175

28.571 21.164 3.175 2.116 15 13.714 1.114 0.086 30.24

26.667 20.317 3.81 2.032 13.333 12.8 0.427 0.080 31.5

23.111 17.778 2.222 1.556 11.764 11.093 0.578 0.069 36

21.333 16.162 3.232 1.616 13.333 12.8 0.448 0.064 49.5

20.111 14.524 3.910 1.117 13.414 12.549 0.784 0.06 57.28

18.631 14.222 2.702 1.138 11.756 11.179 0.503 0.056 56.25

16.660 13.003 2.235 1.219 13.328 12.795 0.466 0.050 78.75

14.561 10.836 2.201 1.016 11.765 11.183 0.524 0.044 94.5

13.333 9.877 1.877 1.185 16.667 16 0.613 0.04 162

12.504 9.481 1.837 1.067 13.329 12.804 0.475 0.038 135

20.677 15.754 2.462 2.092 16.666 15.880 0.600 0.124 65

H.
DISPLAY

USEC

12.8 2.2 1.2 13.346 12.749 0.498 0.05 80

H.BACK
PORCH

USEC

H.SYNC
WIDTH

USEC

VERT.
TOTAL:

MSEC

V.D IS -

-PLAY

MSEC

V.BACK
PORCH

MSEC

V.SYNC
WIDTH

MSEC

VIDEO
RATE

MHz

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p

y

Front view

3. Control Location and Functions

UltraBrite

Mode

Rear view

UltraBrite Mode

“1” ke

Down

U

Power switc

Power switch

Led indicator

Auto Sizing

“2” key

15 pin D Sub

AC input

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4.1. Function Key adjustment Description:

(a). Power switch: This is a “software “Key, Turns the display on and off. The power indicator will

light “Green”, when the display is on.

“1” key: Turn (on /off) OSD menu.

Key: Down side to select item / decrease value

Key: Up side to select item / increase value

: Keys can directly access Contrast / Brightness adjustment

(b). “ 2 “ key: a select key or go to next sub menu.

(c). Pressing “2 & power” key at same time to switch monitor on and then pressing “1” Key will

enter factory optimized OSD Menu (see Fig. 0)

(d). Selected  icon and then pressing “2” key will demagnetize CDT.

(e). High Brightness Key ( UltraBrite Mode ): this key will be effective only after switching on

monitor
(not in preset state), Pressing this key will switch normal brightness to high brightness.
The next pressing will return to normal brightness.
In preset menu, Sup93 / Sup65 / Sup50 represent the high brightness of 9300K / 6500K /
5000K.

(f). Autosizing Key: pressing this key will automatically adjust the display to a proper setting.

Note this function only work precisely after all preset modes being set up.

For Autosizing reference, all maually set up preset modes must be saved by pressing “head
“ Icon.

Fig. 0 Factory OSD Menu

4.2 User OSD menu descriptions

Press “1” key to display a basic main menu (1) shown as below.

FIGURE 1( USER MODE OSD MENU 1)

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Using and keys to move a cyan window bar to get your desired items. If it is selected,

Then pressing “2” key to display

Sub menu as below to start adjustment.

Using and to decrease / increase value on selected item. Noted that the menu can do two

items adjust

by pressing “2” key, it will change to another one in toggle.

In main menu (1), move the cyan window bar up to the first item or down to the last item, then the

next bar moving will enter main menu (2) as below for other adjustment.

FIGURE 2 ( USER MODE OSD MENU 2)

In main menu 2, if “ VIEWMATCH COLOR” is selected, then pressing “2” key will display

color sub menu as the following

The three default color modes (9300k, 6500k, 5000k) are factory preset, User can select these

default colors but can’t adjust and save.

If “USER COLOR” is selected, then pressing “2” key will display next sub menu as below to start

color adjustment.

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In main menu(2), if “LANGUAGE” is selected, then pressing “2” key will display next sub menu

as below for languages selection

If “view meter” is selected, then pressing “2” key will display next sub menu as below to display

timing information.

Normal brightness / High brightness

(VIEWMETER)

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f

a

4. Disassembly Instructions

Disassembly Instructions

1.Swivel Base Removal

Face down the monitor(Fig 4-1), press the
stopper then slide lift off the swivel base
from the monitor,

2.Back Cover Removal

a) Remove two screws of the lower side o

the back cover.(Fig4-2),(Fig4-3)

b) Use a small flat bladed screwdriver or

paper clip insert into the two respective
crevices which located in the seam of
the front & back cover on the top of the
cabinet.

Hold and Push the tool down to release
the snap-on lock, then remove the back
cover. (Fig 4-4)

4. Disassembly Instructions

Caution : When servicing or replacing the

CRT, disconnects the anode and
discharges the anode shield
completely.
As high voltage (25KV) may remain
on the anode for an extended time
after power off.

3.PCB Assembly Remove

a) Unplug two grounding connectors

and the degaussing coil grounding
connector from the CRT drive
shield.

b) Remove CRT drive board from CRT

neck (Fig 4-5).

c) Unplug the DY connector, AC

connector, Degaussing coil
connector and the CRT grounding
connector from the FBT shield.

(Fig 4-1)

(Fig 4-3)

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(Fig 4-2)

(Fig 4-4)

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d) Discharges the remaining static

e) Remove the PC main board from the

electricity by shorting CRT anode to

ground. Then remove the FBT anode

connector.

(Fig 4-5)

4.CRT Removal

a) CRT is supplied as ITC.

chassis guide of the front cover. (Fig4-6)

(Fig 4-6)

b) Remove 4 screws (F) from the front cover

(Fig4-7) to move the CRT

CAUTION: Do not lift the CRT by the neck.

F

F

(Fig 4-7)

F

F

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5. General Connection & Applications

5-1.The Pin-assignments of the 15pin D-sub male miniature connector are shown below:

1

6

11

15 Pin Min D-sub male connector

PIN NO PIN DESCRIPTION

1 RED

2 GREEN

3 BLUE

4 NO CONNECTION

5 GROUND

6 R-GROUND

7 G-GROUND

8 B-GROUND

9 +5V PC97

10 GROUND

11 NO CONNECTION

12 SDA FOR DDC

13 H.SYNC.

14 V.SYNC.

15 SCL FOR DDC

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5-2 Monitor Installation

How to install the connections to your PC

1. Your monitor has two connection cables:

A signal cable which connects to your computer's VGA connector.

A power cord which connect to the wall outlet.

2. To ensure your safety when connecting the cable, always following these five steps:

(҇) .Turn off the power to your computer and peripheral equipment.

(҈). Position the monitor and computer so that you can easily access the rear side of each unit.

(҉).Connect the blue-colored video signal cable D-sub connector to the signal connector on the graphics

board (VGA connector) on your computer. (See your system user's guide for the exact location of your

VGA connector.)

(Ҋ).Tighten the screws on the signal cable connector to prevent it from loose, and to keep out from radio and

TV interference.

(ҋ).To connect Power Cord between your monitor and wall outlet, you have to connect the power cord to the

monitor power input socket on back of the monitor. Plug the other end of the power cord into your surge

protector or properly-grounded electrical outlet.

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6. Electronic Circuit Description

SWTCHING MODE POWER SUPPLY SECTION

Features:

1. AC input: 100Vac – 240Vac.

2. When Power saving is activated, secondary feedback will be changed to reduce the output voltage and
shut down time-base as well as video circuit operation. Thus power is reduced.

6-1-1. Circuit description:

6-1-2-1 EMI Noise Filter
6-1-2-2

C802 and C803 build as Y capacitors, C804 is X capacitor, L801 and L802 are Common Mode Choke,
those build as a two steps Noise filter.

6-1-2-3 Power supply activation:

The rectified voltage across C809 charges C815 through R809, R810, R811, R812, Q810, and D822.
When UC3842 pin 7 rises up to 14V, Q816 turns on and Q810 turns off. C817 charge to 55Vdc approx.
This voltage is ready for B+ of UC3842 at Pin7 during power save Mode. C844 provides a voltage for UVP
(AC input under voltage protection). When C844 voltage is too low, Q814 turns off, voltage at pin 2 of
UC3842 is over 2.5Vdc, and UC3842 will be turned off to protect power supply.

6-1-2-4 Degaussing circuit

Degaussing coil is connected to relay (SR801), and controlled by MCU through Q104 and Q104A.
When power is turned on, SR801 relay close, automatic demagnetization will operate for a few
seconds before SR801 returns to open. Degaussing also can be operated in the OSD menu.

ʳ

6-1-2-5 UC3842 PWM controller

UC3842 is a current feedback PWM controller:
Pin1---is feedback positive end.
Pin2---190V and 9V at secondary side of power transformer provide a sampling
voltage to pin 2 of UC3842 via I808, I807.
Pin3---is a current feedback input. When it is over 1V, there is no output at pin6 to drive
output stage.
Pin4---This pin determine the operating frequency.
Pin6---This output drive output power MOSFET(Q801).

ʳ

6-1-2-6 Output voltage feedback control theory

Feedback control is sampled from 190Vdc and 9Vdc at secondary side, through VR R827, it feedback to
reference pin of I808, then I807 coupled it to pin 2 of UC3842. When output voltage rise up, I808 reference
voltage (R) rise up too, and I808 cathode (K) voltage goes down. More conduction on I807 occurs and the
voltage across R826 rises. Thus UC3842 pin2 voltage rises to reduce the duty at output pin6. Q801
conduct less to reduce the secondary side voltages, thus to stabilize the DC voltages at secondary side.

ʳ

6-1-2-7 Over-voltage protection

When output voltages are too high, voltage across C817 will be high and voltage drop on R872 is also high.
It will force Q808, Q807 to conduct and pin8 of UC3842 to ground. Thus UC3842 stop to operate.

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ʳ

6-1-2-8 Under-voltage protection

If AC input voltage is too low, voltage across C844 will be too low and force Q814 to turn off. Voltage across
C822 rises up. When pin2 of UC3842 rises up to 2.5V, pin6 stop to drive output. Thus Q801 is protected.

ʳ

6-1-2-9 Power supply working frequency

UC3842 working frequency is constant between 30.25 kHz and 31.25 kHz, R817A adjust the frequency.

6-1-2-10 Power Saving control

At normal operating state, Q811 on, Q812 off, output voltage are normal. If monitor enter power save Mode,
Q811 and Q812 off, feedback voltage increase more to reduce output voltages down to 1/4 of normal.
At power save mode, I805 turns off, R821 become in series with R817A, R817. The working frequency will
be reduced to 15 kHz approx.
When monitor enter power saving state, voltage across C817 start to supply UC3842 at pin7 for continue
working.
Q805, Q806 switch on to supply 5V for MCU(IA01).

6-2 DIGITAL CONTROL CIRCUIT( Signal control by Microprocessor unit; IA01)

Horizontal and vertical sync. Signals coming from CRT drive Board (PWB—0414) are fed into pin41 (H.

sync.) and pin42 (V. sync.) of IA01. When monitor power on, pin4 of IA01 reset and IA01 start to check

if the sync. Signals are exist at pin 41 and pin 42. The control tables are as follows:

Power state Normal Off

Pin42,Pin41V sync. H. sync. H. sync. or V. sync. not

exist, or both not exist

Pin23 Logic high Logic low

I804 OFF ON

Pin24(G) High Low

Pin22(A) Low High

LED Green Amber

.

Off mode:

When both sync. Signals or one of the sync. Signals are absent; IA01 will send a “low logic” at pin 23

and pin21 to turn off Q811, Q812. The secondary voltages will be greatly reduced, and Q867, Q866 are

turned off. The heater voltage becomes zero. Monitor enter lower power consumption.

Normal Power supply operation:

When monitor is switched on, the sync signals are both exist, then IA01 will send “Low logic” at pin 13 to

switch on the relay BR801 via Q104 and Q104A and thus produce a very high current circulate the

degaussing coil. This signal will sustain for a certain period, thus the display is demagnetized.

The sync signals are buffered by IA01 and output at pin 41, 42 to synchronize the time-base controller

I301. IA01 will also initiate I301 by IIC bus build by pin 28(C.SCL), pin 27(C.SDA). This IIC bus is also

responsible to initiate the video pre-amplifier I901and OSD I903. After the initiation is completed, I301,

I901 and I903 will operate normally.

Pin 17 ~ pin 20 provide the logic to control the horizontal CS linear correction circuit according to the

horizontal frequency range as the following table.

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IA01 o/p

Pin20

Pin19

Pin18

Pin17

H. freq.
FH < 32kHz

32kHz < FH d 36kHz

36kHz < FH d 40kHz

40kHz < FH d 45kHz

45kHz < FH d 49.5kHz

49.5kHz < FH d 58kHz

58kHz < FH d 65kHz

65kHz < FH d 70kHz

70kHz < FH d 87kHz

Pin 36 (F/V) provides horizontal C linearity control.

Pin 40 provide rotation signal to rotation circuit build by Q471, Q472 and Q473 and thus control the

current circulate the coil around the deflection yoke to rotate the display.

Pin 31 short to ground via 15pin D sub connector when it connect to PC. When it is not shorted to

ground, power saving feature is switch off, monitor will display “PLEASE CHECK SIGNAL” as self test

pattern. IA02 is E

6- 3 TIMEBASE CIRCUIT

Cs0

Cs1

Cs2

Cs3

H H H H

H L H H

L H L H

H H H L

L H H L

L L H L

H H L L

L H L L

H L L L

2

PROM for IA01 to save settings of all modes and DDC data.

6-3-1 TIMEBASE CONTROL (I301), HORIZONTAL

I301 is an I

2

C control Time-base processor. By I2C bus (pin29,30 (SDA,SCL)) it can communicate with

IA01(MCU).

H. sync, and V. sync. come from pin41, 42 of IA01 to pin1, and 2 of I301. When the H. Freq. is over 89

kHz or below 28 kHz, I301 will shut down to protect the horizontal output CKT from being damaged. The

horizon. Oscillator is built by C303 and R301, and determines the horizontal frequency range. C304,

C305, R302 build up PLL 1 loop filter.

Via Icon, the IIC-bus allows a linear adjustment of the relative phase between horizontal Sync.

and oscillator saw-tooth (in PLL 1 loop).

By and , correction of pin unbalance and parallelogram are done by modulating the phase

between oscillator saw-tooth and horizontal. fly back (in loop PLL2)

The PLL2 phase detector is similar to PLL 1 detector, it compares the Horizontal. Flyback pulse at pin 12

with the oscillator saw-tooth wave-form. The controlled currents are independent of Horizontal. Freq.

The PLL 2 thus compensates for the delay in the output horizontal deflection CKT by adjusting the phase

of the HDRV (pin26) output pulse.

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6-3-2 HORIZONTAL OUTPUT STAGE

The Horizontal Drive Pulse output at pin 26 is pulled up to 12V to drive Q404 and then coupled via T401

to output transistor Q433 for on-off control. Thus saw-tooth current through Horizontal Deflection Yoke is

obtained.

The function of C-correction is to correct the asymmetrical non-linearity of picture. L402 and horizontal

Yoke are in series for C-correction. Pin36 of IA01 provides a voltage which depends on Horizontal

Frequency to control L402 via Q405, thus the inductance of L402 changes according to the Horizontal

Frequency to correct the linearity.

The function of S-correction is to correct the symmetrical non-linear distortion equidistant lines.

C416, C423, C419, C420, C421 are S-correction capacitors, also they block the DC voltage to the Yoke.

C416 is a fixed one; the others are controlled by IA01 via Q417, Q411, Q413, Q415 switches. When any

switch turns on, the accordingly capacitor becomes in parallel with C416. The switches on-off depend on

the Horizontal Frequency. They are:

Horiz. Freq.

70 < fh d 87kHz
65 < fh d 70kHz
58 < fh d 65kHz

49.5 < fh d 58kHz
45 < fh d 49.5kHz
40 < fh d 45kHz
36 < fh d 40kHz
32 < fh d 36kHz
d 32 kHz

C416
Fixed

0.24

C423

controlled

by Q416

0.1(CS0)

ON ON OFF OFF OFF
ON OFF ON OFF OFF
ON ON ON OFF OFF
ON OFF OFF ON OFF
ON OFF ON ON OFF
ON ON ON ON OFF
ON OFF ON OFF ON
ON ON OFF ON ON
ON ON ON ON ON

C419

controlled

by Q410

0.22(CS1)

C420

controlled

by Q412

0.56(CS2)

6-3-3 SUPPLY VOLTAGE CONTROL FOR HORIZONTAL DEFLECTION

The B+ control function block is included in I301 which consists of an operational trans-conductance

amplifier, a voltage comparator, a flip-flop and a discharge circuit. Pin 28 of I301 is a drive voltage which

consists of horizontal width, pincushion, and trapezium and pin corner correction information. This

2

voltage is controlled by IA01 via I

C bus. The drive voltage feed into pin15 (BIN) of I301. The operation

frequency of the B+ control block is the same as horizontal frequency. The B+ drive output of the control

block is at pin 28(B.DRV.), this drive voltage switch Q402 on-off via a buffer build by Q400 and Q401.

Q402 act as a step down DC converter to drive horizontal deflection output Q433 via L401. The width,

pincushion, trapezium information are modulated on the DC converter by changing the duty of the B+

drive.

Moreover, the B+ duty is controlled with a charging circuit at same time. When the Q302 is OFF, the

voltage at pin16 of I301 will linearly increase with a charge time of determining by R326 and C308 to

modulate B+ duty.

Horizontal DC centering circuit is build by Q423, Q424. By controlling the small current flow in or out of

L405, it will provide DC center compensation for CDT.

C421

controlled

by Q414

1.2(CS3)

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6-3-4 TIMEBASE CONTROL (I301), VERTICAL

The vertical free running frequency is determined by C312 (pin 22 of I301). The amplitude of the output

at pin 23 can be adjusted via Icon.

Icon provides a DC shift at the saw-tooth output at pin 23 and the EW drive output EWDRV (pin24)

in such a way, that the whole picture moves vertically while maintaining the correct geometry.

6-3-5 VERTICAL OUTPUT STAGE

The power amplifier driving the vertical yoke assembly is a DC design-based on power amplifier I310

TDA8172.

The vertical deflection coil is connected to pin5 of I310 via P401A.

The saw-tooth signal is derived from Pin 23 of I301 and fed to pin1 of I310 via R306. The DC bias voltage

is derived from pin13 of I301 and fed to pin7 of I310 via derived R325 / R327 to optimize the vertical

position.

There are two supply voltages for I310, -15V is applied at pin4 via R384, +15V DC voltage is applied

through R386 to pin2 and pin6 for the output stage during the retrace time. The supply voltage for the

output stage during the retrace time is derived from the fly-back generator output at pin3 of I310 and

applied through C388 to pin6.

6- 4 HIGH VOLTAGE GENERATOR AND BLANKING CIRCUIT

I101 is a current mode PWM controller which provides the drive signal for high voltage generator. It is

synchronized by horizontal blanking signal coming from deflection circuit via Q111. Q121, Q124 are high

voltage output switches. T101 provide the high voltage (25.9KV) to CDT anode. Pin13 of T101 provides

feedback to pin2 of I101 to control the duty when high voltage is varied according to the beam current.

Thus it gives a very good high voltage and size regulation. A very precise geometry distortion is achieved.

R176 provides high voltage adjustment.

Pin5 of T101 senses high voltage for OVP protection. When high voltage is over 33kV, it raises the emitter

voltage of Q114 to the degree that is 6.8V higher than Q115 collector, Q116 start to conduct and shutdown

the PWM (I101) by reducing the voltage at pin1.

Pin 8 of FBT senses the beam current. When beam current rise, base voltage of Q126 drop and so the

emitter does. The voltage across C108 drops to pull down the voltage at pin15 of I901 (PWB-0414). When

voltage at pin15 of I901 drops under 6V, contrast of display start to decrease. R167 set the light output

where the contrast (or full white screen light output) start to drop. If the beam current is too high, Q118 will

conduct and shutdown PWM controller (I101).

Pin7 of FBT provides negative bias for Grid1 of CDT.

Pin5 of I310 provides vertical blanking to base of Q108 via D113. Q108 collector pulse gives a proper

blanking level at Grid 1 of CDT. When monitor turns off, pin3 (H.UNLOCK) is pull high to turn off Q108 via

D108. Grid 1 of CDT is then pulled down to most negative voltage from pin7 of FBT to protect CDT.

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6- 5 Dynamic focus circuit

The vertical dynamic focus come from pin 32 of I301 and feed to base of Q105 via R105 and C103. The

horizontal dynamic focus is taken between L402 and Horizontal S correction capacitors. It is step

up(amplified) to the certain level voltage (650V approx. at 80kHz Timing Mode) and combine with Vertical

dynamic focus waveform through L403, and then feed to PIN 12 of FBT. The dual trace parabola

wave-form plus the DC focus voltage gives sharp and clear display for the whole screen.

The two variable resistors on top of FBT provide focus setting.

The bottom one set Grid 2 voltage of CDT.

.

6- 6-1 Video and CDT drive circuit

7-6-1 VIDEO PREAMPLIFIER (I901)

The signals come from PC through P901 to CDT drive board (PWB-0414). Pin7 (Red), pin5

(Green), pin3 (Blue) feed to pin11, 6, 2 of I901 (video pre-amplifier). Pin 4, 9, 13 of I901 are OSD R,

G, B video signals input that come from OSD IC I903. Pin 12 of I901 is the input for OSD blanking

signal which blank the normal video as OSD video signal is active. Since the video inputs are AC

coupled to I901, so I901 need a clamping signal (at pin 19) from H. sync (IA01 pin 34) to give DC

restoring at I901 outputs. The horizontal blanking signal is provided from PWB-0334. Via P903, it

connects to pin 27 of I901. The video outputs of I901 will have the level darker than the video black

level during the horizontal retrace time. Pin 20 and 21are I

2

C input for MCU (IA01) to control video.

By IIC bus MCU will initiate I901 and control the contrast, brightness, R/G/B gain, and R/G/B bias.
Pin15 is an ABL control input. By detecting the beam current, it will reduce the contrast when the
beam current exceeds the setting point.

6-6-2 VIDEO DRIVE AND OUTPUT CIRCUITS

After being pre-amplified, the R. G. B. video signals set output at pin35, pin32, and pin29 of I901

respectively. The amplitude of the signal at theses output are about 2.8Vp-p. Those video signals

are connected to I904 at pin 7, 6, 9 respectively.

The I904 is video output amplifier to amplify the R, G, and B signals. They offer about 50 Vp-p (H.B)

signals in amplitude to drive the cathodes of CRT.

L912, L942, L972, are the peaking coils, for the compensation of high frequency response.

The DC off-set bias voltage is set up by R902, R903 at pin30 of I901.

The cathode cut-off setting voltages required for white balance are obtained from pin23 (g), pin25

(r), pin26 (b) respectively, these outputs magnitude can control the conduction of transistors Q903,

Q933, Q963 individually. The DC bias of the cathode is then varied to optimize the color

temperature of background.

Brightness control: Pin 2 of IA01 provides Brightness control. It feed through P903 to base of Q910

to vary R, G, and B bias at cathodes simultaneously.

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