Tatung G5GS Series User manual

MODEL:C5GS
SERIES
Low Radiation Extended VGA
PLUG & PLAY COLOUR MONITOR
SERVICE MANUAL

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TABLE OF CONTENTS
PAGE
1. Precaution and Notices ....................................................................................... 1
2. Specifications ....................................................................................................... 3
3. Control Location and Functions ....................................................................... 5
4. Disassembly Instructions ................................................................................... 7
5. General Connection & Applications ................................................................. 9
6. Electronic Circuit Description ......................................................................... 10
7. Adjustment ........................................................................................................ 19
8. Troubleshooting Flow Chart ............................................................................ 22
9. Block Diagram .................................................................................................. 28
10. PCB Layout ....................................................................................................... 29
11. Circuit Diagram ................................................................................................ 30
12. Electrical Parts List .......................................................................................... 31
13. Mechanical Disassembly .................................................................................. 45
14. Mechanical Parts List ....................................................................................... 46

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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 these displays outside the cabinet or with the cover removed involves a shock hazard
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 equipment.
3) Do not install, remove or handle the picture tube in any manner unless shatter-proof goggles
are worn. People not equipped should be kept away while handling picture tube.
4) The picture tube is constructed to limit X-RADIATION to 0.5mR/HR at 300 microamperes anode
current. For continued protection, use the recommended replacement tube only, and adjust the
voltage so that the designated maximum rating at the anode will not be exceeded.
5) Before returning a serviced display to the customer, a thorough safely 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. Proceed as follows :
Connect the monitor power lead to the mains supply, via an isolation transformer, and switch on.
Using the test circuit shown in Fig.1-1, measure the AC leakage current between each pole ( L
and N) of the supply and all accessible metal parts. The earth leakage current must not exceed 3.5
mA.
L
Mains N
Input E
Connectto
ExposedMetal
Parts
MeasuringCircuit
Resistance=2000 ohms
Fig.1-1 AC Leakage Current Test Circuit
mA

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1.2 Product Safety Notice
1) Many electrical and mechanical parts in this chassis provide special visual safety protection.
The protection afforded by them cannot necessarily be obtained by using replacement
components rated for higher voltage, wattage, etc.
2) 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.
1.3 Service Notes
1) When replacing parts or circuit boards, wrap the wires around terminals before soldering.
2) When replacing a high wattage resistor (more than 1/2 W) on a circuit board, keep the resistor
about 10mm (1/2in.) 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.

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2. Specifications
2.1 Monitor Specification
Power Source AC 100 ~240V , 50 / 60Hz
LED color is green Normal Operation (Max.70W)
LED color is amber Stand By / Suspend Mode (Max.15W)
Power
Consumption LED color is amber Off Mode (Max. 3W)
Picture Tube 15" (Diagonal), glare, non- glare, anti-static, 90°Deflection,
0.28mm dot pitch, Low Radiation, Mini-Gun Tube.
Viewable Image
Size 13.9" (Diagonal)
Horizontal 1024 Pixels (Non-Interlaced)
Maximum
Resolution Vertical 768 Lines (Non- Interlaced)
Input Signals Video Analog 0.7 Vp-p / 75 ohm Positive
Separate Sync.
TTL Level
Horizontal : Positive / Negative
Vertical : Positive / Negative
Synchronization Horizontal 30KHz - 57KHz continuous
Vertical 50Hz - 120Hz continuous
Display Colours Analog Input 16 million colours
Horizontal 260 mm
Active Display
Area Vertical 195 mm
Plug & Play DDC1 / 2B
Operating
Temperature +5• ~ +35•
Operating
Humidity 10 % ~ 80 % (Non-Condensing)
Storage
Temperature -20• ~ +65•
Storage
Humidity 15 % ~80 %
High Voltage 25KV
Dimension Width 360 mm
Height 384 mm (With Base)
Height of Base : 58mm
Depth 388 mm
Weight 11.3Kg (Net weight)/ 13.5Kg (Gross weight)

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2.2 Preset Timing Table(I) for HP
Mode Resolution H-Freq. V-Freq. Hs. pol. Vs. pol.
1 720 x 400 31.47 kHz 70.08 Hz Negative (-) Positive (+)
2 640 x 480 31.47 kHz 59.95 Hz Negative (-) Negative (-)
3 640 x 480 35.16 kHz 56.25 Hz Negative (+/-) Negative (+/-)
4 800 x 600 37.88 kHz 60.32 Hz Negative (+/-) Negative (+/-)
5 640 x 480 37.86 kHz 72.81 Hz Negative (+/-) Negative (+/-)
6 640 x 480 37.50 kHz 75.00 Hz Positive (-) Positive (-)
7 800 x 600 48.08 kHz 72.18 Hz Positive (+/-) Positive (+/-)
8 1024 x 768 48.36 kHz 60.00 Hz Negative (-) Negative (-)
9 800 x 600 53.67 kHz 85.00 Hz Positive (+) Positive (+)
Preset Timing Table(II) for others
Mode Resolution H-Freq. V-Freq. Hs. pol. Vs. pol.
1 720 x 400 31.47 kHz 70.08 Hz Negative (-) Positive (+)
2 640 x 480 31.47 kHz 59.95 Hz Negative (-) Negative (-)
3 640 x 480 37.50 kHz 75.00 Hz Negative (-) Negative (-)
4 640 x 480 43.30 kHz 85.00 Hz Negative (-) Negative (-)
5 800 x 600 46.88 kHz 75.00 Hz Positive (+) Positive (+)
6 800 x 600 53.67 kHz 85.00 Hz Positive (+) Positive (+)
7 1024 x 768 48.36 kHz 60.00 Hz Negative (-) Negative (-)
8 1024 x 768 56.47 kHz 70.00 Hz Negative (-) Negative (-)

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3. Control Location and Functions
3.1 Indication LEDs :
When one of the digital controls is selected, the corresponding LED(s) are lit.
CONTRAST : To adjust the contrast of the display.
BRIGHTNESS : To adjust the brightness of the display.
H-POSITION : Adjust the horizontal position of the entire screen image.
H-WIDTH : Adjust the horizontal width of the entire screen image.
V-POSITION : Adjust the vertical position of the entire screen image.
V-HEIGHT : Adjust the vertical height of the entire screen image.
PINCUSHION : If the vertical sides of the screen image curve in or bulge out,
you can correct the pincushion distortion using this adjustment.
TRAPEZOID : If the picture is wider at the top or bottom, you can correct the
trapezoid distortion by using this adjustment.
PARALLEL : If the sides of the screen image are tilted, you can use this
adjustment to correct the parallel distortion.
ZOOM : This is used to adjust H-width and V-Height, simultaneously.
RECALL : This is used to recall the original factory display settings.
Front View Rear View
1. Indication LEDs 1. AC Power Plug
2. Control Buttons 2. Signal Cable
3. Power Switch's LED
4. Power Switch
1. 2. 3. 4. 1. 2.

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3.2 Control Buttons :
The Select Button (the left button) selects a digital control. The selected control is indicated by
the corresponding indication LED. The Down (down arrow) and UP (up arrow) buttons allow you to
decrease or increase the value of the selected control.
Press the Down (down arrow) and up (up arrow) simultaneously, Then it will degauss the
display.
3.3 Power Switch and LED
Push to power on the monitor and push again to power off. The indicator LED will be green
when the power switch is ON and the power cord is properly connected. The color of the LED
depends on the power state of the monitor. When the LED color is permanently green, it
indicates the monitor is at normal state. And when the power LED is amber, it indicates the monitor
is at a power saving state.
We recommend you switch on the monitor first, before switching on the computer!

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4. Disassembly Instructions
1) Face Down the Monitor : ( Fig.4-1 )
2) Swivel Base Removal : First press the stopper, then slide the swivel ball down and remove it.
( Fig.4-2 )
3) Back Cover Removal : Remove 4 screws (A) ( Fig.4-3 ) and (B) (Fig. 4-4) from the back cover.
Then remove the back cover.
4) PCB Assembly Removal :
CAUTION: When serving or replacing the CRT, disconnect the anode and discharge the anode
completely. As high voltage (25.0KV) may remain on the anode for an extended time after
power off.
( Fig.4-1 ) ( Fig.4-2 )
(A) (B)
( Fig.4-3 ) ( Fig.4-4 )
Stopper

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a) Unplug grounding connectors and the degaussing coil grounding connector from the CRT
drive shield.
b) Remove CRT drive board (C) 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.
d) Discharge the remaining static electricity by shorting CRT anode and ground, then remove
the FBT anode connector.
f) Press two clips(D) from left and right side of front cover(Fig.4-5) to remove main chassis.
5) CRT Removal :
CAUTION : Do not lift the CRT by the neck.
a) CRT is supplied as ITC.
b) Remove 4 screws (E) from the front cover (Fig.4-6) to move the CRT.
(C)
(D) (E) (E)
( Fig.4-5 ) ( Fig.4-6 )

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5. General Connection & Applications
Procedure for installing and using your Multi-Sync. display.
5.1Connecting the monitor to the computer
1) Set up the display at the desired operation location , on top of or beside your personal computer.
Plug the power cord into the monitor and then connect the other end of the power cord into an
AC outlet. The three-wire power cord is shielded type and is provided as a safety precautions to
ensure proper electrical grounding.
2) Connect the 15-pin color display shield signal cable to the video adapter output on your
computer, then lock both screws to ensure proper grounding. The connector information is as
follows :
PIN Description
1 Red
2 Green
3 Blue
4 Open
5 Return
6 Red Ground
7 Green Ground
8 Blue Ground
9 +5V ( PC97)
10 Ground
11 Open
12 SDA
13 H.Sync.
14 V.Sync.
15 SCL
3) First turn the PC power switch ON.Then apply power to the display by pressing the Power
ON/ OFF Switch to turn the monitor on. The power indicator LED will illuminate.
Allow about five seconds for the display tube to warm up, data will be displayed on screen.
NOTE : Don't force the cable into the connector; line it up carefully so that you don't bend the pins.

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6 . Electronic Circuit Description
6.1 Switching Mode Power Supply ( SMPS )
The switching mode power supply for this monitor is a full range type, i.e. universal power input
of AC 100V ~ 240V is compatible. When AC input is supplied through the slow blow fuse F801, the
line choke L803 to the rectifier D811 ~ D814, the rectified DC voltage is about 125V ~ 335V and then
fed to the switching transformer T801.
Prior to start, a small current flows to C808 via R828 and R831. I801 is to operate immediately
when the voltage across C808 reaches 16V. At the same time, Q801 is on, the rectified current flows
through the primary winding of T801 and the energy is stored in it .
When Q801 is off, the stored energy is transferred to the secondary winding, the auxiliary
winding is close-coupled and in phase with the secondary winding. It will provide a holding voltage
on C808 and fed to pin7 of I801 via R820 and D808. I801 will keep working provided that the voltage
across C808 is over 10V. The oscillating frequency of the switching mode power supply is around
20KHz, which is determined by the timing components R822 and C813. C813 is charged to 2.8V via
the 5V reference voltage at pin8 of I801and discharged to 1.2V during the discharged time interval.
The oscillator generates a series of blanking pulses, which cause the output at pin6 of I801 to go low.
The fly-back pulse from T403 is applied via D816 and R807 to force C813 to discharge, so that
the oscillating frequency is synchronized and kept in phase with that of horizontal frequency to avoid
interference on display screen.
In case of voltage variations due to the change of input AC or output loading, the auxiliary
winding will reflect these variation to pin2 of I801 via D818, R812, R813, I803 and I802. The voltage
at pin2 of I801 is compared with the internal 2.5V reference voltage to produce an error voltage inside
I801.
This error voltage is limited to 1V by internal Zener diode and is compared with the voltage at
pin3 of I801 which is supplied from the voltage detected across R825 and R823, while Q801 is on.
Q801 is off only when the voltage drop across R825 and R823 has reached that of the error voltage, or
1 Vp-p maximum, that is, the duty cycle of the pulse width modulator is controlled by the combined
error voltage to regulate the output voltage.

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If over-load or short circuit occurs at the secondary, the voltage across R825 and R823 reaches
1Vp-p rapidly, thereby blocking the power output, the voltage at pin7 of I801 then decrease to below
10V, I801 is forced off.
However, in order to allow auto-recovery from power saving off state, the SMPS circuit is
designed as an unlatched type, the DC current flows via R828, R831, Q813 and D828 to charge C808
again. When the voltage across C808 has reached 16V, I801 is turned on again. Once the peak voltage
across R825 and R823 is over 1Vp-p, I801 will be forced off again. Consequently, I801 is turned on
and off repeatedly, under this situation, if the power does not be switched off, Q801, R825 and R823
may finally be over stressed and fail.
6.2 Power Management Circuit
Power
Switch I201 STATE I201 #40 (Vs) I201 #39 (Hs) I201 #29 (PM1) I201 #28 (PM2) D891 LED
NORMAL 1 1 1 1 GREEN
STAND BY 1 0 0 1 AMBER
SUSPEND 0 1 0 1 AMBER
ON
OFF 0 0 0 0 AMBER
OFF x x 1 0 OFF
When the display signal enters into "Stand By" or "Suspend" state of power saving, with either H.
Sync. or V. Sync. off, the voltage at pin29 of I201 is low, both Q808 and Q809 are switched off to
block the 16V voltage supply, thereby shut down the oscillation of the horizontal and vertical
deflection, power conservation is achieved.
When the display signal enters the "Off" state of power saving with both H. Sync. and V. Sync.
off, the voltage at pin28 and pin29 of I201 are low, then all Q805, Q806, Q808 and Q809 are switched
off. 11V and 16V voltage supply for the loading circuit are blocked. The overall power dissipation is
significantly reduced to less then 3W watt.
Automatic recovery from "Off" state to "NORMAL" state is achieved once the recovery H. Sync.
and V. Sync. trigger I201 via R254 and R256, the voltage at pin28 and 29 of I201 will go high again to
turn on Q809, Q806 via Q808 and Q805.
Power Indicator
The power indicator D891 is composed of two LED in one. The 5V voltage is applied through
R244 to lighten the Green LED and through R243 to lighten the Yellow LED of D891. D891 is
controlled by the power management voltage, result in Green or Amber color for Normal or Stand By,
Suspend, Off State respectively.

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Heater Voltage
The heater element in the CRT is supplied with 6.3±0.3V during normal operation and reduced
to 5.0±0.5V during Stand By or Suspend state. To achieve this, Q805, Q806 and associated circuit is
introduced, when at normal state, PM2 is HIGH level then Q805 ON, to trigger Q806 ON, 10V from
D815 to Q806, R841, R991 and heater, the heater voltage is 6.3V±0.3V.
When at Suspend, Stand-Bystate the horizontal output is shut down, there is no horizontal pulse,
PM1 is Low level, the feedback voltage at pin2 of I801 is higher than that of normal state. This will
force the output voltage at secondary side of T801 drop down, the heater voltage is reduced to 5.0±
0.5V .
6.3 Automatic Degaussing Circuit
The posistor R803 and the degaussing coil L891 comprise an automatic degaussing circuit to
demagnetize the shadow mask and the internal shield of the CRT in order to protect the display screen
from color impurity.
The resistance value of the posistor is originally low (7 ohm) during power off. Right after the
display is powered-on, the voltage at pin26 of I201 is HIGH, then Q803 ON and RL01 triggered a
large AC current flows through the posistor into the degaussing coil for demagnetization.
Meanwhile, the resistance of the posistor increase rapidly due to rising of its temperature, the
degaussing current thus decreases to less then 100mAp-p in a few seconds so that display screen
settles quickly, degaussing function is then complete. After 5 seconds, the voltage at pin26 of I201 is
LOW, then Q803 OFF and RL01 release.
6.4 Micro Control Circuit
MTV212AN32 / MTV212AN64
The monitor uses an advanced CPU I201 to control the Contrast, Brightness, H. Position, H.
Width, V. Position, V. Height, Pincushion, Trapezoid and Parallelogram, Zoom, Recall.
The horizontal sync. and vertical sync. are via R254, R256 then fed to pin39, pin40 of I201. The
output sync signals are fed to pin1 and pin2 of deflection processor I401 via pin33, pin32 of I201.
The control signals on pin1, pin2 are for PWM (Pulse Width Modulation) which are converted
into DC voltages via integration circuits. With the Brightness control signal as an example, the PWM
control signal is derived from pin2 of I501 which is fed into a integration circuit R209, C202

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and pull-up resistor R208. The other control function is by I2C-bus, the SCL and SDA signals are fed
to pin30 and pin31 of deflection processor I401 via pin10 pin9 of I201.
The CPU is reset by the components C204, C203 and D213 at pin4 of I201, when the AC source
is connecting, every time to ensure correct start.
The +5 voltage is fed into I201 via pin5, a 12MHz resonator (or crystal) is connected at pin7,
pin8 of I201 to generate the CPU clock for the software execution. The user key control input is fed to
the A/D converter at pin22, pin23 via R229, R231, R257,R258 and S201•S202.
The function indictors are connected to pin16 ~ 21 of I201. The control signal for horizontal
linearity circuit is derived from pin14 of I201 which is fed to the CS circuit Q425, Q424.
There is a low power override pin on pin15 of I201, this pin is connected to pin12 of the signal
cable P501. When the signal cable is disconnected from the computer, this pin is high, and the power
saving function will be disable. Meanwhile, the CPU I201 will activate the self-test signal from pin11
to generate a Self-Test Pattern. When the signal cable is connected to the computer, this pin is
low and the power saving function will be enable, the CPU can generate a power saving signal control
voltage at pin29 and pin28 of I201. Note that, the Self-Test Pattern will not appear once the signal
cable is connected to the computer.
The monitor is design to have the DDC 1/2B functions, communication between the monitor and
computer for DDC is via pins24, 25 of I201 which are defined as SDA, SCL signals. The computer
will read out the EDID data from the EEPROM I202 via I2C data lines. The EDID data is written into
the EEPROM in the factory during production. The memory size for EDID data is 128 bytes
which is shared from EEPROM 1202 which has 4K bytes memory size.
6.5 How to enter into the factory setting ?
The monitor includes 9 factory preset timings for HP, or 8 factory preset timings for others, the
preset mode timing detect by the Mcu I201 Pin.37. although only some of the timing are fine tuned by
auto alignment during production.
Switch off the monitor, push and hold down the Select control key , power on again, wait 1.0
second then release the Select key, the monitor should now be in the factory setting mode, all the
LEDs will now be illuminated. Selection of function will be indicated by the extinguishing of the
appropriate LEDs, All adjustment data will be stored automatically, then power on again, the monitor
will reverse to normal operating state.

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6.6 Deflection Processor
6.6.1 I401 is used for S1D2511B
I401 S1D2511B is a Samsung monolithic integrated circuit assembled in a 32 pins shrunk dual
in line plastic package. I401 controls all the functions related to the horizontal and vertical deflection
in a multi-sync monitor. All functions are controllable by I2C-bus.
6.6.2 Pin-Out Description for S1D2511B ( I401 )
PIN SYMBOL DESCRIPTION
1 H/HVIN TTL compatible horizontal sync input (Separate or composite)
2 VSYNCIN TTL compatible vertical sync input (for separated H&V)
3 HLOCKOUT First PLL lock/ unlock output (0V unlocked, 5V locked)
4 PLL2C Second PLL loop filter
5 C0 Horizontal oscillator capacitor
6 R0 Horizontal oscillator resistor
7 PLL1F First PLL loop filter
8 HPOSITION Horizontal position filter (Capacitor to be connected to HGND)
9 HFOCUSCAP Horizontal dynamic focus oscillator capacitor
10 FOCUSOUT Mixed horizontal and vertical dynamic focus output
11 HGND Horizontal Section Ground
12 HFLY Horizontal flyback Input (positive polarity)
13 HREF Horizontal Section Reference Voltage (to be filtered)
14 COMP B+ error amplifier output for frequency compensation and gain setting
15 REGIN Regulation input of B+ control loop
16 ISENSE Sensing of external B+ switching transistor current or switch for
step-down converter
17 B+GND Ground (related to B+ reference adjustment)
18 BREATH DC breathing input control (Compensation of vertical amplifier against
EHV variation)
19 VGND Vertical section ground
20 VAGCCAP Memory capacitor for automatic gain control loop in vertical ramp
generator
21 VREF Vertical section reference voltage (to be filtered)
22 VCAP Vertical sawtooth generator capacitor
23 VOUT Vertical ramp output (with frequency independent amplitude and S or C corrections if any). It is mixed with vertical position voltage and vertical
moire
24 EWOUT Pincushion-East/ West correction parabola output
25 XRAY X-RAY protection input (with internal latch function)
26 HOUT Horizontal drive output (internal transistor, open collector)
27 GND General ground (referenced to Vcc)
28 BOUT B+ PWM regulator output
29 Vcc Supply voltage (12V typ)
30 SCL I2C clock input
31 SDA I2C data input
32 5V Supply voltage (5V typ)

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6.7 Vertical Deflection Circuit
The power amplifier drive the vertical yoke assembly is a DC design based on power amplifier
I301 TDA8172.
The TDA8172 consists of a differential input stage, two power supply (+10V and –11V), a
flyback generator, a protection circuit for the output stages. The differential input stage has a high
CMRR differential current mode input (pin6 and pin7 ). This differential sawtooth signal is derived
from pin21, 23 of I401.
The flyback voltage will be generated internally by doubling the supply voltage and therefore a
separate flyback supply voltage is not needed.
The Vout (pin 5) provides a blanking signal for the CRT via D302, R301, R302.
6.8 Horizontal Deflection Circuit
The product designed around a base-drive circuit driving horizontal deflection circuit to provide
sufficient switching current. Q401 is switched by the horizontal drive signal from pin8 of I401 via
R427, C475. This produces a sufficient voltage to T401, snubber network R448, C410 compensates
for leakage inductance in T401 and shapes the base drive waveform.
The drive signal is fed to Q403 via D431,R431, R430. When Q403 is at the "Off" state, the
voltage which is stored on the base of Q403 discharge via R431, D431. The drive signal control Q403
switch on-off, so that saw-tooth waveform current flows in the horizontal deflection coil is obtained.
The positive horizontal fly-back pulse signal derived from pin6 of T403 is fed to pin1 of I401 via
R411, this fly-back signal provides proper timing reference for horizontal drive output.
The horizontal deflection output circuit combine the transistor switching function with a
damping diode to generate saw-tooth waveform current flow through the deflection coil.
The basic horizontal deflection output circuit comprises switching transistor Q403, fly-back
transformer T403 , damper diode which included D413, D414 tuning capacitor C413, modulation
capacitor C414, S-shape correction capacitor C415 / C452 and linearity coil L402.

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When the horizontal frequency of input signal is greater then 42.4KHz, Q425 is on, Q424 is off,
C415 is the only capacitor for S-shape correction.
Input H.
Frequency I201#17 Cs C415 C452
Fh < 42.4KHz 0 ON ON
42.4KHz < Fh 1 ON OFF
6.9 Horizontal Width Control
The monitor uses a diode modulation circuit for the control of horizontal width, it is achieved by
changing the base voltage of Q418, the control voltage (0~ 5V) is from pin11 of I401 via R454,
which consist of horizontal pincushion & corner correction & DC shift & trapezium correction. There
are controlled by I2C-bus via I201, low DC shift voltage will cause large width control current flows
out pin11 of I401 via R454 and then the horizontal width is increased.
6.10 Pincushion and Trapezoid Control
The combined pincushion and trapezoid control signal output from pin11 of I401 is applied to
the base of Q418 via R454. This parabolic signal modulates the horizontal width automatically. So
that dynamic pincushion correction ( DPC ) and trapezoid distortion correction are achieved .
6.11 Spot Killer Circuit
The spot killer circuit is included, in order to prevent CRT from spot damage while switching
power on or off. -160V derived from pin7 of T403 is applied via D449, R490, R487 to collector of
Q406. When power is off, -160V is fed to G1 via R490 and R488 to cut off the beam current.
On particular occasion, when X-ray protection is activated, pin17 of I401 go high, then Q402 is
turn-off, Q406 turn-off, -160V is fed to G1 via R490 , R488 to cut off the beam current.
6.12 Brightness Control Circuit
The brightness control voltage derived from pin2 of I201 is applied via R209, R407 to control
the bias of Q402 and Q406, G1 voltage is changed accordingly to obtain desired screen brightness.
6.13 Blanking Circuit
The vertical blanking pulse derived from pin5 of I301 and pin14 of I401 are applied via D302
and D301 respectively and combined together through R303 to cut off Q402, Q406. This blanking
signal is fed to G1 via R490, R488 to prevent retrace lines from appearing on the display screen.

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6.14 H.V. Control Circuit
The horizontal feedback signal derived from pin6 of T403 is applied via D403, R415, R420,
R402, R416 and peak-detected by C474 and R492, then fed to the error amplifier on pin5 of I401, the
value of R410 is chosen to have a suitable gain for the error amplifier.
The saw-tooth waveform signal related to the output current of Q413 is fed to pin4 of I401 via
R451 for current mode regulation.
Both of the horizontal feedback signal and saw-tooth waveform signal are fed to a comparator in
I401 to generate a PWM ( Pulse Width Modulation ) control signal at pin6 of I401 , this square
waveform control signal is then fed to Q413 via buffer Q412. Q413 is designed as a step-up voltage
converter, the DC voltage is fed to the Drain of Q413 via L417, the energy is stored in L417 when
Q413 is on , and released when Q413 is off.
The circuit supplies DC voltage ( 90V ~ 190V ) to pin9 of T403 for horizontal scanning via
Q413 and D440, this supply voltage is approximately proportion to the horizontal frequency in order
to keep the scanning amplitude constant when the horizontal frequency changes. The snub circuit
consists of C442, R442, R441, C441 is for noise limitation.

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6.15 Video Circuit
The analog R. G. B. video input signals are supplied through the cable which is terminated at
P501, these input signals are approximately 0.7 Vp-p in amplitude.
R501/ R531/ R561 give a resistance of 75 ohm for impedance matching. The R. G. B. video
signals are AC coupled via C501/ C531/ C561 then fed into the video pre-amplifier I501 at pin6, pin3
and pin1 respectively.
R503/ R533/ R563 act as R. G. B. video gain control. DC bias to the video gain controls are
through R502/ R532/ R562 which are connected to 12V voltage.
After being pre-amplified, the R. G. B. video signal are output from pin14, pin17, pin20 of I501
respectively. Signal amplitude at these output are about 3 ~ 4 V p-p.
The DC contrast control voltage from R584 is applied to pin9 of I501 which varies the AC gain
of all three R. G. B. channel amplifiers simultaneously. C582 added at pin9 of I501 to prevent noise
entering into the IC.
The video output amplifiers are composed of typical cascode stages. Q901/ Q902, Q931/ Q932,
Q961/ Q962 amplify the video signals to amplitude level of about 35 ~ 45 Vp-p, which is enough to
drive the CRT cathodes. The feedback emitter resistors R901/ R902, R931/ R932, Q961/ Q962 and
the emitter peaking capacitors C902/ C932/ C962, the peaking coils L901/ L902, L931/ L932, L961/
L962 are for frequency response compensation.
The cathode cut off voltage settings required for white balance are achieved by adjusting R910/
R940 / R970.
The series surge limiting resistors R908/ R938/R968 for the video amplifiers will form a
low-pass-filter with the CRT capacitance, therefore offering protection against flash-over.