AOC VGA1581 User manual

15" CDT Color Monitor VGA1581
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Service
Service
Service
Horizontal Frequency
30-56 kHz
TABLEOFCONTENTS
Description Page Description Page
SAFETY NOTICE
ANY PERSON ATTEMPTING TO SERVICE THIS CHASSIS MUST FAMILIARIZE HIMSELF WITH THE
CHASSIS AND BE AWARE OF THE NECESSARY SAFETY PRECAUTIONS TO BE USED WHEN SERVICING
ELECTRONIC EQUIPMENT CONTAINING HIGH VOLTAGES.
Table Of Contents...................................................1
Revision List.......................................................2
Important Safety Notice.................................3
1. Specifications..........................................4
2. Precaution And Notices................................6
2-1safety Precautions....…...............…..............6
2-2 Product Safety Notice ..........................................6
2-3 Service Notices....................…………......7
2-4 High Voltage Warning............................................7
3. Operating Instructions................…….............8
4. Adjustment ..................…………...............9
4 -1. Adjustment Conditions And Precautions ...……........9
4-2. Main Adjustments.....................…………........9
4-3 Adjustment Methods........................................9
5.Circuit Description ..………………………............12
5-1.Micro Controller And Deflection Circuit .....…………...12
5-2.Transistor & Diode Circuit...............................14
6. Trouble Shooting Chart...........................…….............15
6-1.No Raster......……………………………….….....….....15
6-2. Abnormal Displays................………….…...….....…17
6-3. Hor./OSC/DEF/HV Circuit Fault................................18
6-4. Abnormal Horizontal Deflection...............................18
6-5. Abnormal Vertical Scanning............….....................19
6-6. Side-Pin Cushion Distortion.......………….........19
6-7. Poor Focus................................................19
6-8. Power Supply Trouble Shooting Chart.................20
7. Block Diagram.....................................................21
8. IC Block Diagrams...............................................23
9. PCB Layout.......................................................27
9-1 Main PCB Layout.................................................27
9-2 CRPC Board Layout...........................................29
10. Schematic Diagram.........................................30
11. Mechanical Of Cabinet Front Dis-Assembly..........31
12. BOM List...................…………............................32
CAUTION: USE A SEPARATE ISOLATION TRANSFOMER FOR THIS UNIT WHEN SERVICING

15" CDT Color Monitor VGA1581
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Revision List
Revision Release Date Change Instruction TPV model
A00 Nov-27-06 Initial release D555DJCCWSNBRP

15" CDT Color Monitor VGA1581
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Important Safety Notice
Proper service and repair is important to the safe, reliable operation of all AOC Company Equipment. The service
procedures recommended by AOC and described in this service manual are effective methods of performing
service operations. Some of these service operations require the use of tools specially designed for the purpose.
The special tools should be used when and as recommended.
It is important to note that this manual contains various CAUTIONS and NOTICES which should be carefully read
in order to minimize the risk of personal injury to service personnel. The possibility exists that improper service
methods may damage the equipment. It is also important to understand that these CAUTIONS and NOTICES ARE
NOT EXHAUSTIVE. AOC could not possibly know, evaluate and advise the service trade of all conceivable ways in
which service might be done or of the possible hazardous consequences of each way. Consequently, AOC has not
undertaken any such broad evaluation. Accordingly, a servicer who uses a service procedure or tool which is not
recommended by AOC must first satisfy himself thoroughly that neither his safety nor the safe operation of the
equipment will be jeopardized by the service method selected.
Hereafter throughout this manual, AOC Company will be referred to as AOC.
WARNING
Use of substitute replacement parts, which do not have the same, specified safety characteristics may create shock,
fire, or other hazards.
Under no circumstances should the original design be modified or altered without written permission from AOC.
AOC assumes no liability, express or implied, arising out of any unauthorized modification of design.
Servicer assumes all liability.
FOR PRODUCTS CONTAINING LASER:
DANGER-Invisible laser radiation when open AVOID DIRECT EXPOSURE TO BEAM.
CAUTION-Use of controls or adjustments or performance of procedures other than those specified herein may
result in hazardous radiation exposure.
CAUTION -The use of optical instruments with this product will increase eye hazard.
TO ENSURE THE CONTINUED RELIABILITY OF THIS PRODUCT, USE ONLY ORIGINAL MANUFACTURER'S
REPLACEMENT PARTS, WHICH ARE LISTED WITH THEIR PART NUMBERS IN THE PARTS LIST SECTION
OF THIS SERVICE MANUAL.
Take care during handling the LCD module with backlight unit
-Must mount the module using mounting holes arranged in four corners.
-Do not press on the panel, edge of the frame strongly or electric shock as this will result in damage to the screen.
-Do not scratch or press on the panel with any sharp objects, such as pencil or pen as this may result in damage to
the panel.
-Protect the module from the ESD as it may damage the electronic circuit (C-MOS).
-Make certain that treatment person’s body is grounded through wristband.
-Do not leave the module in high temperature and in areas of high humidity for a long time.
-Avoid contact with water as it may a short circuit within the module.
-If the surface of panel becomes dirty, please wipe it off with a soft material. (Cleaning with a dirty or rough cloth
may damage the panel.)

15" CDT Color Monitor VGA1581
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1. Specifications
1. CRT : 38 cm (15”) F&S high contrast CRT, 0.28mm dot pitch, 90 degree, Shadow mask, non glare, anti-
static coating
2. Viewable image Size: 15” F&S (13.8” visual) diagonal
3. Display Color: Unlimited Colors
4. External Controls:
Power On/Off, OSD key, Function knob: Contrast, Brightness, H-Size, H-Center, V-Center, V-Size,
Pincushion, Trapezoid, Pin-Balance, Parallelogram, Rotation, 6500 Color Temperature, 9300 Color
Temperature, Degauss, Moire Reduce, Recall, Language, Zoom, User color, Language,Exit.
5. Input Video Signal
Factory preset #1 #2 #3 #4 #5
H-Resolution [Pix]: 720 640 800 1024 640
V-Resolution [Lines]: 400 480 600 768 480
Pixel-Clock [MHz]: 28.320 25.168 56.248 65.000 36.000
H-Frequency [kHz]: 31.327 31.460 53.670 48.363 43.269
V-Frequency [Hz]: 69.616 59.924 84.414 60.004 85.008
IBM VGA VESA VESA VESA
6. Display Size
Horizontal: 270 mm±4.0mm
Vertical: 200 mm±4.0mm
7. Scanning Frequencies
Horizontal: 30KHz ~ 56KHz
Vertical: 50 Hz ~ 120 Hz
8. Factory Preset Timings: 5
User Timings: 12
9. Misconvergence
Zone A(height circle) 0.30 mm Max.
Zone B(elsewhere) 0.40 mm Max.
10. Video Bandwidth: 65 MHz
11. Power Source:
Switching Mode Power Supply
AC 90 ~264V, 50 ±3 Hz , 60 ±3 Hz Universal Type
12. Operating Temperature: 0°C to 40°C Ambient
13. Operating Humidity: 10% (20%) to 85% Relative
14. Main Dimensions / Weight
Monitor Packed Monitor
Width: 360mm 460mm
Height: 362mm 425mm
Depth: 387mm 494mm
Weight: 11.5kg 14.0kg

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15. Power Consumption
Mode H-SYNC V-SYNC Video Pw-cons. Indicator
Power-On on On active < 75W Green LED
Power-off off On blanked < 8W Orange LED
Power-off on Off blanked < 8W Orange LED
Power-off off Off blanked < 8W Orange LED
16. External Connection:
15 Pin D-type Connector
AC Power Cord
17. Safety And EMC
- EN 60950 + EK1/59-98,EK1/60-98: GS-mark
- UL1950
- CSA 22.2 No.950
- VDE 0860 (implosion protection)
- CE-mark
- CB-certificate and test report according to IEC950
The model is designed to reach following approvals:
- EN 55022 class B and EN 55024
- FCC class B part 15
- GB9254 and GB17625.1
Test scope and test results for the immunity measurements
Measurement Norm Test result
Disturbance by means of electrostatic discharges IEC61000-4-2
EN61000-4-2 passed
Disturbance by means of electromagnetic in the frequency
range from 80 MHZ up to 1000 MHZ
IEC61000-4-3
EN61000-4-3 passed
Disturbance by means of fast transients(EFT) IEC61000-4-4
EN61000-4-4 passed
Disturbance by means of fast surge(1,2µS /50µS) IEC61000-4-5
EN61000-4-5 passed
Disturbance by means of RF-voltage IEC61000-4-6
EN61000-4-6 passed
Disturbance by means of voltage dips and drops IEC61000-4-11
EN61000-4-11 passed
Measuring procedure to prove the immunity against magnetic
fields with technical frequency
IEC61000-4-8
EN61000-4-8 passed
Test scope and test results for the emission measurements
Measurement Norm Test result
Measurement of the interference voltage(line conduction test)
in the frequency range from 150kHz up to 30 MHZ EN55022:1998 passed
Measurement of the radiated interference in the frequency
range from 30 MHZ up to 1000 MHZ EN55022:1998 passed
Measurement of low-frequency harmonics EN61000-3-2:1995
passed
Measurement of the variations in line voltage and flicker EN61000-3-3:1995
passed

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2. Precautions And Notices
2-1 Safety Precautions
1. Observe all caution and safety related notes located inside the display cabinet.
2. Operation of the display with the cover removed, may cause a serious shock hazard from the display
power supply. Work on the display should not be attempted by anyone who is not thoroughly familiar
with precautions necessary when working on high voltage equipment.
3. Do not install, remove or handle the picture tube in any manner unless shatter-proof goggles are worn.
People who are not so equipped should be kept away while handling picture tube. Keep picture tube
away from the body while handling.
4. The picture tube is constructed to limit X-RAY radiation to 0.5 mR/HR. For continued protection, use the
designated replacement tube only, and adjust the voltages so that the designated maximum rating at the
anode will not be exceeded.
5. Symbol“ !“ means safety relative parts. The use of substitute replacement parts which do not have
the same characteristics as specified in the parts list may create shock, fire or explode etc.
6. Symbol“”means X-ray relative parts. Before replacing any of these components please read the
parts list in this manual carefully to avoid creating higher anode voltage or x-ray. Especially for sealed
controls, such as VR902, VR903, VR701 and FBT screen VR etc, which were sealed by the
manufacturer once their optimum position has been set, please don’t dismantle them as your likes,
otherwise you will break or damage the component. If you need replace the parts with sealed control,
please adjust the relative VR to make sure the B+ voltage under 59V and well seal it with A+B glue or
equivalent, which you can not move away with one screw driver
7. Before returning a serviced display to the customer, a thorough safety test must be performed to verify
that the display is safe to operate without danger or shock. Always perform an AC leakage current
check on the exposed metallic parts of the cabinet, such as screw heads.
Test method for current leakage is described as follow.
(a) Plug the AC line cord directly into rated AC outlet (do not use a line isolation transformer during this
check).
(b) Use an AC voltmeter having 5000 ohms per volt or with more sensitivity in the following manner:
Connect a 1500 ohms 10 Watt resistor, paralleled by a 0.15UF, AC type capacitor between a
known good earth ground (water pipe, conduit, etc.) and the exposed metallic parts simultaneously.
Measure the AC voltage across the combination of 1500 ohms resistor and 0.15UF capacitor.
(c) Reverse the AC plug at the AC outlet and repeat AC voltage measurements for each exposed
metallic part.
(d) Voltage measured must not exceed 0.5 volts RMS. This corresponds to 0.35 milliamp AC. Any
value exceeding this limit constitutes a potential shock hazard and must be corrected immediately.
2-2 Product Safety Notice
Many electrical and mechanical parts in this chassis have special safety visual inspections and the protection
afforded by them cannot necessarily be obtained by using replacement components rated for higher voltage,
wattage, etc. Before replacing any of these components read the parts list in this manual carefully. The use
of substitute replacement parts which do not have the same safety characteristics as specified in the parts
list may create shock, fire, X-RAY radiation or other hazards.

15" CDT Color Monitor VGA1581
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2-3 Service Notes
1. When replacing parts or circuit boards, clamp the lead wires around terminals before soldering.
2. When replacing a high wattage resistor (more than 1/2W of metal oxide film resistor) in circuit board,
keep the resistor about 10mm (1/2 in) away from circuit board.
3. Keep wires away from high voltage or high temperature components.
4. Keep wires in their original position so as to reduce interference.
2-4 High Voltage Warning
Operation of monitor outside of cabinet or with back removed may cause a serious shock hazard. Work on
this model should only be performed by those who are thoroughly familiar with precautions necessary when
working on high voltage equipment.
Exercise care when servicing this chassis with power applied. Many B plus and high voltage terminals are
exposed which, if carelessly contacted, can cause serious shock or result in damage to the chassis. Maintain
interconnecting ground lead connections between chassis and picture tube dag when operating chassis.
Certain HV failures can increase X-ray radiation. Monitor should not be operated with HV levels exceeding
the specified rating for the chassis type. The maximum operating HV specified for the chassis used in this
monitor is
25KV ±0.8KV
with a line voltage of 120/240 VAC. Higher voltage may also increase possibility of failure in HV supply.
It is important to maintain specified values of all components in the horizontal and high voltage circuits and
anywhere else in the monitor that could cause a rise in high voltage or operating supply voltages. No
changes should be made to the original design of the monitor. Components shown in the shaded areas on
the schematic should be replaced with exact factory replacement parts. The use of unauthorized substitute
parts may create a shock, fire or other hazard.
To determine the presence of high voltage, use accurate, high impedance, HV meter connected between
second anode lead and CRT dag grounding device. When servicing the High Voltage System, remove static
charge from it by connecting a 10K ohm resistor in series with an insulated wire (such as a test probe)
between picture tube dag and 2nd anode lead.(AC line cord disconnected from AC power outlet.)
The picture tube used in this monitor employs integral implosion protection. Replace with tube of the same
type number for continue safety. Do not lift picture tube by the neck. Handle the picture tube only after
discharging the high voltage completely.

15" CDT Color Monitor VGA1581
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3. Operating Instructions
This procedure gives you instructions for installing and using the Color display.
1. Position the display on the desired operation and plug the power cord into a convenient AC outlet. Three-wire
power cord must be shielded and is provided as a safety precaution as it connects the chassis and cabinet to
the electrical conduit ground. If the AC outlet in your location does not have provisions for the grounded type
plug, the installer should attach the proper adapter to ensure a safe ground potential.
2. Connect the 15-pin color display shielded signal cable to your signal system device and lock both screws on
the connector to ensure firm grounding. The connector information is as follow:
15 - Pin Color Display Signal Cable
Pin No. Description Pin No. Description
1. Red Video 9. No Pin!
2. Green Video 10. Logic Ground
3. Blue Video 11. No Pin!
4. No Pin! 12. DDC-Serial Data
5. No Pin! 13. H-Sync.
6. Red Ground 14. V-Sync.
7. Green Ground 15. DDC-Serial Clock
8. Blue Ground
3. Apply power to the display by turning the power switch to the "ON" position and allow about thirty
seconds for display tube warm-up. The Power-On indicator lights when the display is on.
4. With proper signals feed to the display, a pattern or data should appear on the screen, adjust the
brightness and contrast to the most pleasing display.
5. This monitor has power saving function following the VESA DPMS. Be sure to connect the signal cable
to the PC.
6. If your color display requires service, it must be returned with the power cord.
1
6
11 15
5
10

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4. Adjustment
4-1 Adjustment Conditions And Precautions
1. Approximately 30 minutes should be allowed for warm up before proceeding.
2. Adjustments should be undertaken only on those necessary elements since most of them have been
carefully preset at the factory.
4-2 Main Adjustments
No. Function Location Designation
1. B + ADJ PCB - MAIN VR902
2. SCREEN ADJ FLY BACK TRANS T402
3. FOCUS ADJ FLY BACK TRANS T402
- MENU PCB - MAIN SW103
-UP PCB - MAIN SW102
4. Function Adj
-DOWN PCB - MAIN SW101
4-3 Adjustment Method
1. B + voltage adjustment:
A. CHROMA-2000 Signal generator or PC equivalent set TIMING 16, VESA 640X480 pattern 1.0 .
B. Connect a DC Volt meter between D925”-” polarity and ground, then adjust VR902 to be 81±0.5V.
C. Make the screen size for H = 270mm V=200mm .
D. Readjust VR902 and make the voltage of D25 ”-” polarity for 84V ±0.5V .
2.External Controls
1
2
3
4
5
6
7
8
9
10
11
12
13
NO. Switch NO. Functions NO. Functions
1. Power On/Off Switch 6. Contrast 11. V-Center
2. LED 7. Brightness 12. Pincushion
3. Up Key 8. H-Size 13. Trapezoid
4. Down Key 9. H-Center 3+4. Recall
5. Function Key 10. V-Size 12+13. Rotation
LED1 LED2 LE3 LED4 LED5 LED6 LED7 LED8 LED7+ LED8
( +)=

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3. Factory preset timings adjustment:
A. When you turn on the monitor, the function LEDs will light Up simultaneously for a while, then
extinguish.
B. You can press hold the Up/Func tow key simultaneously turn on the monitor, the most left four LEDs
will light Up for a while then exitinguish
C. Input Geometric factory mode, then you can select one of the sixteen Functions, Including, Contrast,
Brightness, H-Size, H-Center, V-Size, V-Center, Pincushion, Trapezoid, Rotation, V-Moire, H-Moire,
Pin-Balance, Parallelogram, Corner, V-Linear and V-Linear Balance Simply, Press the Function key
and the LED will be light UP corresponding to the one selected, then press the Up/Down keys to get
the factory presetting parameter value to your satisfaction.
D. Then change mode or power turn off, the display setting will be saved.
E. Then you will press the turn OFF monitor again, the factory preset timings adjustment is finished.
F. Function Control LED Display Fashion:
1.Contrast
2.Brightness
3.R-Bias
4.G-Bias
5.B-Bias
6.R-Gain
7.G-Gain
8.B-Gain
9.ABL
10.VE
11.HE
4. White Balance add Luminance adjustment:
A. Function keys specification:
Press UP and DOWN and Power on keys, LED5, LED6, LED7, LED8 are lighting, then all LEDs are on /off.
Choose the function, Press UP and DOWN to adjust it. The detailed LED adjustment as following:
1.Contrast
2.Brightness
3.R-Bias
4.G-Bias
5.B-Bias
6.R-Gain
7.G-Gain
8.B-Gain
9.ABL
10.VE
11.HE
B.Adjusting process instruction
1.Degaussing firstly, turn on the power and enter the white balance setting mode, then warm it up until steadily.
2.Raster Max adjustment: set Chroma 2000 at Timing 106,Raster Pattern as 104,G-Bias fixup 4F.Brightness and
contrast at max, adjust the R-bias and FBT Screen button, test screen center to set the grounding as 2.5+-
0.2cd/m2, X=265±10; Y=290±10 according to brightness
3.Raster Cut off adjustment: set Chroma 2000 at timing 106,pattern 104, and press brightness function key to
make Raster just cut off, Y=0.10+-0.02cd/m2.
4.small window adjustment: set Chroma 2000 as timing 102, pattern 105,adjust R- gain，G-gain，B-gian to
make Y=150±2 cd/m2 X = 283 ±10,Y = 297 ±10
5.Full white screen adjustment: set Chroma 2000 as timing 129, pattern 105, adjust ABL to make Y=90±2 cd/m2 .

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5. Focus Adjustment:
A. Set mode6 640×480@60Hz with character full page.
B. Set for under RECALL state .
C. Then adjust focus VR1 of FBT to the best focus.
D. After focus adjustment ,fix Focus VR, G2 VR use the white lacquer.
6. Purity Adjustment
A. Be sure that the display is not being exposed to any external magnetic fields.
B. Ensure that the spacing between the Purity, Convergence, Magnet, (PCM), assembly and the CRT
stem is 29mm. (See below diagram)
C. Produce a complete, red pattern on the display. Adjust the purity magnet rings on the PCM assembly to
obtain a complete field of the color red. This is done by moving the two tabs in such a manner that they
advance in an opposite direction but at the same time to obtain the same angle between the two tabs,
which should be approximately 180'.
C. Check the complete blue and complete green patterns to observe their respective color purity. Make
minor adjustments if needed.
Relative Placement Of Typical Components
Purity Magnets
Deflection Yoke
4-pole Convergence Magnets
6-pole Convergence Magnets
7.Convergence adjustment
A. Produce a magenta crosshatch on the display.
B. Adjust the focus for the best overall focus on the display.
Also adjust the brightness to the desired condition.
C. Vertical red and blue lines are converged by varying the angle between the two tabs of the 4 pole
magnets on the PCM assembly. (See above diagrams)
D. Horizontal red and blue lines are converged by varying the two tabs together, keeping the angle
between them constant.
E. Produce a white crosshatch pattern on the display.
F. Vertical green and magenta lines are converged by varying the angle between the two tabs of the 6-
pole magnets.
G. Horizontal green and magenta lines are converged by varying the two tabs together, keeping the angle
between them constant.

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5. Circuit Description
5-1 Micro Controller And Deflection Circuit
MICRO Controller
The micro controller(IC101) core is a 80C51 type. The micro clock frequency of 12 Mhz is derived from the
Xtal oscillator, which is running at 48MHz. The DDC interface is suitable to handle DDC2 by a modified
hardware I2C-bus interface .Standard high current ports,3 ADC pouts with voltage inputs and 4 static standard
8 bit DAC outputs (low interference) and one PWM output for digital control application are implemented. The
central processing unit (CPU) manipulates operands in two memory spaces. These are the 1024byte internal
data memory(consisting of 256 bytes standard RAM and 768 bytes AUX-RAM) and 48K-byte internal program
memory . The programmemory of the SAA4848 consists of 48K bytes ROM.
The SAA4848P provides sync. Processing with full auto sync. Capability, a flexible SMPS block and an
extensive set of geometry control facilities. Further the IC generates the drive waveforms for DC coupled
vertical boosters to the TDA4863A.
H/V sync signals processor
The functions of the sync processor include polarity detection, H-SYNC & V-SYNC signals counting,
Programmable SYNC signals output, free running signal generator. Pin52/Pin53 are for the H-SYNC and V-
SYNC input. and the polarity are setting in the positive. When no signal input, the Pin49 will output a 75Hz V-
SYNC free run signal. The Pin18/20will output a 60KHz H-SYNC free run signal. for the monitor testing use.
Reset Circuit(pin23)
There are three ways possible to invoke a reset and initialize the SAA4849 micro controller part:
Via power-on reset circuit
Viawatchdogtimeroverflow(only micro controller reset)
Via deflection reset after start up(only micro controller reset)
The reset pin(pin23) is connected to a Schmitt trigger for nose reduction. A reset is accomplished by holding
the Reset pin HIGH.
2.7K
R153
+
22U
C145
0.1UF
C102
5V RST Pin23

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x-ray protection
The x-ray protection(pin22) input XRAY provides a voltage detector with a precise voltage input for X-ray
protection .If the input voltage at XRAY exceeds the upper threshold for 150us to 300us,the system is forced to
shut down by switching off vertical-and B-drive signals. There are two different ways to handle the system in
case of XRAY occurrence:
1. If the xray latch enable bit UCXRAY[2] was set to “0” during startup the system will shut down without any
interference of the uC.The deflection controller is set to ldle mode. Restart of the system only possible due to
switching power off/power on.
2. If register bit UCXRAY[2] was set to “1”,micro controller interaction is allowed .If the micro controller doesn’t
interrupt the system, the system will shut down to ldle mode. For any interaction of the micro controller the
XRAY occurrence has to be acknowledged by the micro controller by clearing the bit SY-STATUS[2].The micro
controller take over the control of the handling via software. The actual x-ray pin status can be read through bit
SY-STATUS[1].
Quartz Oscillator(pin45,pin46)
The quartz oscillator circuit is available on pins XTAL1(input) and XTAL2(output) and works together with an
external 48MHz 3rd overtone quartz. As a result the quartz oscillator is always running on 48MHz.Other quartz
crystal frequencies than 48 MHz cannot be used. External capacitors on XTAL1 and XTAL2 are not allowed.
B+ Control Function Block
The B+control block of the SAA4848 has the same behaviour as the TDA4863 with adapted threshol
voltages. The circuit allows the user to choose the trigger edge of the HDRV signal and the polarity of the
output stage via I2C-Bus.
The B+ control function block of the SAA4848 consists of an Operational Transconductance Amplifier(OTA),
a voltage comparator, a flip-flop and a discharge circuit. This configuration allows easy application for different
B+ control concepts.
HPLL
The horizontal part contains a PLL,which works over the full frequency range from 25kHz to 140 kHz. This
range can be reduced by a ower and an upper frequency limit(Write Once Registers HPMAX and HPMIN).Via I2C
bus the number of 48MHz clock cycles is sent through the register. The slewing speed during mode change is
also programmable in a write once register (HSLEW)
After the clocks for the HPLL are switched on, the HPLL starts with a fixed forerunning frequency of 60 kHz.
The H-drive pulses are not active and the start up procedure is inhibited. The default setting of register bit
HCONTROL [0] will cause the HPLL to slew ,not switch. to the forerunning frequency defined in the I2C register
HPFREE( the default value is also 60 kHz).Independent on H-syncs which are possibly present. the HPLL will
slew to that forerunning frequency. To achieve an always defined starting point for the startup procedure, this
procedure cannot be interrupted.

15" CDT Color Monitor VGA1581
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5-2 Transistor & Diode Circuit
Location Circuit Function Description
D901 ~ D904 Bridge Rectifier for AC Source
D919 Rectifier for Output Voltage
D913 Rectifier for Output Voltage
D922 Rectifier for Output Voltage
D923 Rectifier for Output Voltage
D925 Rectifier for B+ Supply
Q911 MOS FET for Switching B+ Control.
Q912, Q906 Push-Pull Topology to Drive Q911
Q913 Degaussing Switcher Transistor
Q907 6.3V Regulator Transistor
Q401 Turn-on at Power ON/OFF and Change Mode to Protect Hor.Block
Q402 HOR. Driver Transistor
Q403 HOR. Transistor
Q420,Q423 Horizontal s correction control MOSFET
Q406 Transistor for H-Size Control
Q705 Brightness Control CKT

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6.Trouble Shooting Chart
6-1 No Raster
1.Relative Circuit Problems About CRT
BRIGHTNESS SET TO MAX.
THEN CHECK CRT G1 VOLTAGE
N
G
N
G
N
G
LESS THAN 300V
N
G
N
G
OK
OK
OK
OK
OK
CHECK THE HIGE VOLTAGE
CHECK THE VOLTAGE OF CRT
HEATER ABOUT 6.3V
CHECK VOLTAGE OF THE CRT
CHECK BRIGHTNESS CIRCUIT
CHECK POWER SAVING CIRCUIT,
"ABNORMAL DISPLAY"
CHECK FBT. D706, R725, C713
Q801 RELATIVE CKT.
REFER ITEM 6-2
CATHODE ABOUT 60V TO 70V
CHECK MAIN PC BOARD
CHECK SCREEN VOLTAGE ABOUT
400V TO 600V
OF CRT ABOUT 23.5KV ~ 24.5KV
Q908, Q910
RELATIVE CIRCUIT Q907, Q909
CHECK CRT'S HEATER
85V, 12V
CHECK FAILSAFE CKT Q402, Q403
RELATIVE CKT.

15" CDT Color Monitor VGA1581
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2.Abnormal Video Level On Screen
O
K
N
G
O
K
N
G
N
G
O
K
O
K
CHECK THE VOLTAGE OF IC801
CHECK THE SIGNAL INPUT OF
ABOUT 0.7V
pp
CHECK THE VIDEO OUTPUT OF
R.G.B.APPROACH STANDARD
CHECK SIGNAL CABLE O
R
INTERFACE CARD.
CHECK THE RELATIVE CIRCUIT
OF CLAMP.
CHECK IC801
PIN 7 ABOUT 5V
CHECK IC801 PIN 17 ABOUT 5Vpp
CHECK 5V RELATIVE CIRCUIT
PIN 14, 16,18 ABOUT 3V
pp
3.Abnormal DDC (Plug & Play)
O
K
N
G
CHECK IC101 PIN 16 VOLTAGE ABOUT 5V
CHECK SIGNAL CABLE
CHECK IC102 GOOD OR FAIL

15" CDT Color Monitor VGA1581
17
6-2 Abnormal Display
1.No Signal On Screen
CHECK FBT RELATIVE CIRCUIT
LESS THAN 400V
EXCEED 600V
O
K
N
G
N
G
O
K
O
K
N
G
O
K
N
G
CHECK THE OUTPUT VOLTAGE
CHECK THE B+ VOLTAGE OF
CHECK THE VOLTAGE OF CRT
CATHODE ABOUT 40Vpp
CHECK THE VOLTAGE OF FBT SCREEN
ABOUT 400 TO 600V
CHECK THE RELATIVE CIRCUIT
OF SMPS ON MAIN PCB
RELATIVE CIRCUIT
OF P802 CONNECTOR
CHECK THE 85V RELATIVE CIRCUIT
VIDEO PCB ABOUT 85V
CHECK THE IC802
OF IC801
CHECK CRT RELATIVE CIRCUIT
OR REFER ITEM 6-1
CHECK VIDEO IC VCC ABOUT 5V
CHECK THE 12V PIN 10
OF IC801 PIN 14, 16, 18 ABOUT 3V
pp

15" CDT Color Monitor VGA1581
18
6-3 Hor./Osc/Def/Hv Circuit Fault
No Raster (Disconnect With Signal Cable)
N
G
O
K
O
K
O
K
N
G
N
G
N
G
CHECK THE COLLECTOR VOLTAGE
CHECK THE COLLECTOR VOLTAGE
RELATIVE CIRCUIT
RELATIVE CIRCUIT
OF Q402 ABOUT 12.5Vpp
CHECK Q402, T401
CHECK T401, T402, Q402, Q403,
OF Q403 ABOUT 1250Vpp AT FH:31KHz
D408, C418, C419, H-DY, B+
CHECK IC101 PIN16 ABOUT 5 VDC
CHECK IC101 PIN 20 WAVE
FORM ABOUT 1Vpp
CHECK IC101 PIN20 RELATIVE CIRCUIT
CHECK IC401 PIN 39~41
6-4 Abnormal Horizontal Deflection
1.Abnormal Horizontal Size
N
G
OK
CHECK THE RELATIVE CIRCUIT
CHECK THE RELATIVE
CIRCUIT OF SMPS.
CHECK FBT VOLTAGE ABOUT
OF Q404, Q405, & Q406
CHECK THE HV OF CRT
ABOUT 24KV
READJUST H-SIZE FUNCTION
80V AT FH=31KHz
2.Abnormal Horizontal Video Center
RELATIVE CIRCUIT
N
G
SET H-CENTER TO CENTER
CHECK IC101 PIN39,41

15" CDT Color Monitor VGA1581
19
3.Abnormal Horizontal Linearity
CHECK L401, Q420,
C423, C425 & DY IC101 PIN10(CS2)
6-5 Abnormal Vertical Scanning
1.Abnormal Vertical Size
OK
N
G
OK
N
G
READJUST V-SIZE FUNCTION VALUE
READJUST V-SIZE FUNCTION VALUE
CHECK VERT. OSC CIRCUIT
RELATIVE CIRCUIT
CHECK THE VOLTAGE OF IC101
N
G
RELATIVE CIRCUIT
CHECK THE IC601 ABOUT 12V PIN1
CHECK D601, C609 RELATIVE CIRCUIT
CHECK IC101 PIN 33.34
2.Vertical Center
READJUST V-CENTER FUNCTION VALUE
N
G
CHECK IC101 & IC601 RELATIVE CKT
6-6 Side-Pin Cushion Distortion
READJUST SIDEPIN FUNCTION
VA L U E
N
G
RELATIVE CKT.
CHECK IC101, Q406
6-7 Poor Focus
READJUST FOCUS CONTROL
NG CHECK FOCUS CONTROL UNIT, FOCUS
LEAD WIRE, CRT SOCKET & CRT

15" CDT Color Monitor VGA1581
20
6-8. Power Supply Trouble Shooting Chart
BEFORE CHECK SW.REG. PLEASE REFER TO THE POWER SUPPLY BLOCK DIAGRAM
POWER SUPPLY OUTPUT: (A) VARIABLE OUTPUT : 75V - 160V
(DEPENDING EPENDING UPON H.SYNC FREQUENCY)
(B) CONSTANT OUTPUT : 6.3V, 15V, -12V, 75V
BEAD SET ABNORMAL VARIABLE OUTPUT
N
G
OK
N
G
OK
OK
N
G
N
G
OK
OK
N
G
OK
N
G
YES
N
O
CHECK BRIDGE
RECTIFIED CIRCUIT
6.3V CIRCUIT
CHECK START C.K.T
(IT SHALL BE 5V)
R939
CHECK IC101
CHECK D919
CHECK Q911
Q911 FAILURE
CHECK IC101Pin16
CHECK Q901
CHECK IC901
CHECK AC LINE
VOLT 120V OR 220V
CHECK F901, SW901
CHECK LINE RECTIFIED
& SMOOTHED VOLT
CHECK T901 O/P
MAKE SURE THAT
THE VARIABLE
OK
OUTPUT IS NOT SHORTED
CHECK 57V LINE
CHECK 57V, 12.5V