Tatung Vibrant VM78F User manual

17-inch Color Monitor
VM78F
Service Manual

VM78F
Table of Contents
1. Precautions .................................................................................................................2
2. Product Specifications ..............................................................................................5
3. Operation Theory.....................................................................................................10
4. Alignments and Adjustments...................................................................................15
5. Troubleshooting........................................................................................................19
6. Recommended Spare Parts List..............................................................................26
7. Block Diagram..........................................................................................................28
8. Exploded Diagrams ........................................................................................ Inserted
9. PCB Diagrams ................................................................................................ Inserted
10. Schematic Diagrams ...................................................................................... Inserted

PrecautionsPage 2
VM78F
1Precautions
Follow these safety and servicing precautions to prevent damage and to protect against potential hazards
such as electrical shock and X-rays.
1-1 Safety Precautions
1-1-1 Warnings
1. For safety purpose, do not attempt to modify
the circuit board, and always disconnect the AC
power before performing servicing on the
monitor.
2. Operation of the monitor outside its cabinet or
with the cover removed involves the risk of
shock hazard. Repair work on the monitor
should only be attempted by service personnel
who are thoroughly familiar with all necessary
safety precautions and procedures for working
on high voltage equipment.
3. Do not lift the CRT by the neck. After
completely discharging the high voltage anode,
handle the CRT only when wearing shatterproof
goggles. Try to keep the CRT away from the
body during handling.
4. High voltage should always be kept at the rated
value, no higher. Only when high voltage is
excessive are X-rays capable of penetrating the
shell of the CRT. Operation at high voltages
may also cause failure of the CRT or high
voltage circuitry.
5. The CRT is especially constructed to limit X-
ray emission to 0.5mR/HR at 300
microamperes anode current. To ensure
continued X-ray protection, replace the CRT
with only the same or equivalent type as the
original, and adjust the anode’s voltage to the
designated maximum rating, never to exceed.
1-1-2 Safety Checks
Before returning the monitor to the user, perform
the following safety checks:
1. Inspect to make certain that each lead dress is
not pinched or that hardware is not lodged
between the chassis and other metal parts in
the monitor.
2. Inspect all protective devices such as
nonmetallic control knobs, insulating materials,
cabinet backs, adjustment and compartment
covers or shields, isolation resistor-capacitor
networks, mechanical insulators, etc.
3. AC Leakage Current Check
Always perform the AC Leakage Current
Check on the exposed metal parts, including
metal cabinets, screwheads and control shafts,
as follows:
a) Plug the AC line cord directly into a rated
AC outlet. Do not use an isolation
transformer during the check.
b) Use an AC voltmeter with at least 5000
ohms per volt sensitivity as follows:
Connect a 1500 ohms, 10 watt resistor
paralleled by a 0.15uF AC capacitor in series
with all exposed metal cabinet parts and a
known earth ground, such as electrical
conduct or electrical ground connected to
earth ground, as shown in the Figure 1-1.
Measure the AC voltage across the
combination of resistor and capacitor.
c) Reverse the AC plug at the AC outlet and
repeat the steps for AC voltage
measurements for each exposed metal part.
d) Voltage reading must not exceed 0.3 volts
RMS,equivalentto0.2milliampereAC. Any
value exceeding this limit will constitute a
potential shock hazard and must be
corrected immediately.
Figure 1-1. Set Up For AC Leakage Current Check
To known
earth ground
1500 ohm 10 watt
0.15ufd
To exposed metal
cabinet part

Precautions Page 3
VM78F
1-1-3 Product Safety Notices
Many electrical and mechanical parts in this chassis have special safety-related characteristics which are
often not evident from visual inspection, the protection afforded by them may not be obtained by replacing
them with components rated for higher voltage, wattage, etc. Before replacing any of these components,
consult the Recommended Spare Parts List given at the end of this manual. Any of the replacements that do
not provide the same safety characteristics may result in shock, fire, X-ray emission or other hazards.
1-2 Servicing Precautions
Warning: An electrolytic capacitor installed with the wrong polarity might explode.
Caution: Before performing servicing covered by this service manual, read and follow the Safety Precautions
section of this manual.
Note: If there are any unforeseen conflictions between the following servicing precautions and any of
the safety precautions, always follow the safety precautions.
1. Follow closely the servicing precautions printed on the monitor cabinet and chassis.
2. Always unplug the AC power cord from the AC power source before removing or installing any component
or assembly, disconnecting PCB plugs or connectors and connecting a test component in parallel with a
capacitor.
3. When replacing parts or circuit boards, clamp the lead wires around the component before soldering.
4. When replacing a high wattage resistor (>0.5W metal oxide film resistor) in the circuit board, keep the
resistor about 1 cm (1/2 inch) away from the circuit board.
5. Keep wires away from the high voltage or high temperature components.
6. Keep wires in their original positions so as to minimize interference.
7. Always connect a test instrument’s ground lead to the instrument chassis ground before connecting the
positive lead; always remove the instrument’s ground lead last.
After putting the rear cover back on and making sure the monitor is working properly, the Hi-
Pot & Ground Continuity tests MUST BE performed before the monitor is returned to user.
1-3 Hi-Pot Test
1. Test Equipment
Puncturetest model PM5530 ADTorKIKUSUTOS-8750 voltage testerorequivalentapproved equipment.
Note : The test equipment must be calibrated in regular period.
2. Test Setup
a) Apply voltage : DC 2100 VDC
b) Test duration : 3 seconds
c) Cutoff current should be set to 3 mA
3. Test Procedure
a) Unplug power cord from AC source.
b) Put the power switch of the monitor in the “ON” position.
c) Leave signal cable un-connected.

PrecautionsPage 4
VM78F
d) Plug monitor power cord to the Hi Pot tester terminals.
e) Turn on tester and watch the indicator or beeper.
f) If the indicator lamp lights, or beeper beeps, the test fails.
1-4 Ground Continuity Test
1. Test Equipment
AC low ohm tester TOS-6100 or equivalent approved equipment.
Note : The test equipment must be calibrated in regular period.
2. Test Setup
a) Test duration : 3 seconds
b) Set current limit at 25 A
c) The grounding resistance must be less than 0.1 ohm.
3. Test Procedure
a) Plug the monitor power cord to the tester terminals.
b) Make sure all connections are well-contacted.
c) Turn on monitor power and tester power.
d) Press “Test” button.
e) If green light shows up, means test OK.
If red light shows up, means test fails.
f) If the Tester has a digital display, the resistance value must not exceed 0.1 ohm.
Note : Be sure not to touch the metal portion of the signal cable head during testing.

Product Specifications Page 5
VM78F
2Product Specifications
2-1 Specifications
Note: Above specifications are subject to change without prior notice.
Picture Tube 17-inch (15.8-inch Visual image area), sloted mask, 90 degrees deflection, dot type black matrix, medium short persistence
phosphor, dark tint, non-glare/ anti-static screen,
0.25 mm(FNSL/T) dot pitch
Scanning Frequency VGA, Super VGA, 1024x768@60/70/75/85/100 Hz
1280x1024@60/75 Hz
Maximum Resolution 1280 dots (H) x 1024 lines (V) @75Hz refresh rate
Display Area 310 mm (H) x 230 mm (V) typical
Display Characters 80 char. x 60 rows on a 10 x 10 matrix
Display Colors Analog
Input Unlimited Colors
Synchronizatin Signals Separate Sync: horizontal/vertical, TTL, positive or negative
Synchronization
Frequencies Horizontal : 30 to 86 kHz Vertical : 50 to 120 Hz
Signal Connectors 15-pin, D-shell connector
Video Signals Analog : 0.7 Vp-p, RGB positive
Power Input 75 Watts (maximum) AC rated voltage, 100VAC to 240VAC
Misconvergence Center Area : <0.3 mm; Corner Area : <0.4mm
User Controls Power On/Off, Contrast, Brightness, Horizontal Size, Horizontal
Position, Vertical Size, Vertical Position, Pincushion, Trapezoid,
Rotation, Color temperature, Language, Display Frequency,
Degauss, Recall, H. Moire,V. Moire, Pincushion Balance,
Parallel, OSD Position, Top Corner, Bottom Corner
Service Controls PWB-1619
PWB-1620 : power voltage adjust (VR801)
Preset Modes 12 (see Table 2-2. Timing Chart)
Environmental
Considerations Operation temperature : 10oC to 40oC ambient Operation Humidity : 20% to 80% ambient
Storage temperature : -40oC to 65oC ambient
Storage Humidity : 10% to 90% (non-condensing)
Altitude : Non operating 40,000 feet sea level
operating 10,000 feet sea level

Product SpecificationsPage 6
VM78F
2-2 Signal Cable Pin Connections
Table 2-2. Signal Cable Pin Assignment
Pin Signal Pin Signal
1Red video 9** +5V
2Green video 10 Digital Ground
3Blue video 11 Ground
4Ground 12 SDA
5* NC 13 H-Sync
6Red ground 14 V-Sync/VCL
7Green ground 15 SCL
8Blue ground
Note * This pin is used for selftest detection. Connect this pin to ground at the PC end.
** For PC 99: This pin will provide +5V from PC side.

Product Specifications Page 7
VM78F
2-3 Timing Chart
This section describes the timings that the computer industry recognizes as standard for computer-generated
video signals.
Table 2-3. Timing Chart
Seperate Sync
Horizontal
Video
C
D
E
Sync
A
B
F
Vertical
Video
I
J
Sync
G
H
L
K
H.Parameters:
A: Period B: Blanking Time
C: Sync Width D:Back Porch
E: Active Time F: Front Porch
V.Parameters:
G: Period H:Blanking Time
I: Sync Width J: Back Porch
K: Active Time L: Front Porch
MODE 1 2 3 4 5 6 7 8 9 10 11 12
H.Dots 720 640 800 640 800 1024 800 1024 1280 1024 1280 1280
V.Lines 400 480 600 480 600 768 600 768 1024 768 1024 960
H.Freq. (KHZ) 31.47 31.47 37.88 43.27 46.8 48.36 53.67 60.02 64.34 68.68 80 85.938
V.Freq. (HZ) 70.08 59.95 60.32 85 75 60 85 75.03 60 85 75 85
A Period (us) 31.78 31.78 26.4 23.11 21.333 20.68 18.63 16.66 15.55 14.56 12.504 11.636
B Blking (us) 6.356 6.356 6.4 5.33 5.172 4.923 4.409 3.657 3.589 3.725 3.022 3.017
C Sync. (us) 3.81 3.81 3.2 1.556 1.616 2.092 1.138 1.219 0.972 1.016 1.067 1.077
D B.P. (us) 1.907 1.907 2.2 2.22 3.232 2.462 2.702 2.235 2.248 2.201 1.837 1.508
E Active (us) 25.42 25.42 20 17.78 16.162 15.75 14.22 13 11.96 10.836 9.481 8.62
F F.P. (us) 0.636 0.636 11.556 0.323 0.369 0.569 0.203 0.374 0.508 0.119 0.431
G Peroid (ms) 14.27 16.68 16.58 11.76 13.333 16.67 11.76 13.33 16.67 11.77 13.329 11.764
H Blking (ms) 1.557 1.43 0.739 0.67 0.533 0.786 0.578 0.533 0.642 0.582 0.525 0.593
I Sync. (ms) 0.064 0.064 0.106 0.069 0.064 0.124 0.056 0.05 0.047 0.044 0.038 0.035
J B.P. (ms) 1.08 1.02 0.607 0.578 0.448 0.6 0.503 0.466 0.501 0.524 0.475 0.547
K Active (ms) 12.71 15.25 15.84 11.09 12.8 15.88 11.18 12.8 16.03 11.18 12.804 11.171
L F.P. (ms) 0.413 0.35 0.026 0.023 0.021 0.062 0.019 0.017 0.094 0.015 0.013 0.012
CLOCK(MHZ) 28.3 25.1 40 36 49.5 65 56.25 78.75 107 94.5 135 148.5
Sync H--+-+ + + + + + + +
Polarity V+-+-+ + + + + + + +

Product SpecificationsPage 8
VM78F
2-4 Display Power Management Signal (DPMS)
Note: These power-saving states exceed the Environmental Protection Agency (EPA) Energy Star
requirements.
Table 2-4. Display Power Management Signal (DPMS)
* For power consumption : 75W Max. (@ 230V AC, preset size and maximum light output condition)
2-5 TCO Version
The monitor meets the TCO 95/99, NUTEK energy saving, electric and magnetic field requirements.
Also it is compliant with TCO 95/TCO 99 labelling scheme.
The emission from magnetic and electric field must comply with the limits specified by the Swedish Board
for Measurement and Testing, commonly known as MPR 1990 recommendations. These limits are
summarized in the Table 2-4.
Table 2-5. TCO 95 Emission Requirements
VLF/TCO ELF/TCO
Magnetic Field 25 nT 200 nT
Electric Field 1 V/m 10 V/m
Frequency Range 2~400 kHz 5~2000 Hz
Value RMS RMS
Distance 30 cm 30 cm
Electrostatic
Potential +/- 500 V +/- 500 V
The monitor is designed with selected CRT and carefully routed wires around CRT, make sure exactly the
same routing scheme is used when doing CRT replacement.
State LED Color H-Sync V-Sync Power
Consumption
ON Green Pulse Pulse Normal*
OFF Amber No Pulse No Pulse <5 watts

Product Specifications Page 9
VM78F
2-5-1 TCO 95 Version (Optional)
The TCO 95 scheme is for international and environmental labelling of personal computers. The labelling
scheme was developed as a joint effort by the TCO (The Swedish Confederation of Professional Employ
ees), Naturskyddsforeningen (The Swedish Society for Nature Conservation) and NUTEK (The National
Board for Industry and Technical Development in Sweden).
1)`Scope
TCO 95 touches on ergonomic qualities, emissions (electrical and magnetic fields), energy efficiency and
ecology (with demands for environmental adaptation for both the product and the production processes at
the manufacturing plant).
2) Environmental Requirements
The monitor abides by the environmental demands concerning restrictions on the presence and use of
heavy metals, brominated and chlorinated flame retardants, CFCs (freons), and chlorinated solvents,
among other things. The monitor is also recyclable.
3) Energy Requirements
The monitor also follows the energy requirements that, after a certain period of inactivity, the monitor shall
reduce its power consumption to a lower level in one or more stages.
4) Others
The monitor meets the strict environmental demands for the reduction of electric and magnetic fields,
physical and visual ergonomics and good usability.
Table 2-5-1. TCO 95 Visual Ergonomics
Feature Standard Description
Linearity 1% or less Difference in length of columns or rows compared to the
corresponding lengths through the center of the monitor.
Display Luminance 100 cd/m2 (at least)
Luminance
Uniformity 1.7:1 or less The ratio is between the max to min luminance within the whole active area.
2-5-2 TCO 99 Version
TCO 99 will append the color temperature and energy efficiency specification, also cover the environmen-
tal requirement.

Page 10 Operation Theory
VM78F
3Operation Theory
This is a fully digital controlled multi-sync color monitor that is compliant with DDC1 and 2B Plug and Play
VESA standard and offers the following main features.
3-1 Main Features
1. Simplified design with minimum components.
2. The MYSON MTV212 M(A) 32 processor-- that has I2C BUS controlled geometric correction, contrast
and brightness-- offers the functions for: (a) Contrast, (b) Brightness, (c) H-size, (d) H-position, (e) V-
size, (f) V-position, (g) Pincushion, (h) Trapezoid, (i) Pincushion Balance, (j) Parallel, (k) Top Corner and
(l) Bottom Corner.
In addition, it also offers more functions as: (a) Sync. processor, I/P and O/P, (b) Mute, (c) Power saving
- Suspend & Stand-By, (d) Power saving override, (e) DDC1/2B, (f) I2C Bus for auto-alignment through
signal cable (g) CS1/CS2/CS3/CS4 for linearity and size compensation.
3. Stores up to 10 factory preset modes and offers 8 user modes. There are 16 function icons at OSD. They
are controlled by two function keys and flywheel knob on front panel.
4. Powerful PHILIPS TDA4863 and TDA4841 present the following useful functions: (a) Pincushion, (b)
Trapezoid, (c) V-Position, (d) V-Size, (e) Vertical’s “C” and “S” correction -- factory adjust, (f) Pincushion’s
V. position correction, (g) Corner correction -- factory adjust, (h) Pincushion unbalance correction --
factory adjust, (i) Parallelogram distortion -- factory adjust, (j) Moire cancellation, (k) X-ray protection,
and (l) Full horizontal and vertical auto sync capability.
5. Software controlled auto shut off function activated if fH < = 29 kHz and fH > = 86 kHz.
6. Full range AC input and simplified line filter design.
3-2 Microcontrol Section
1. This monitor uses MYSON MTV212 M(A) 32 CPU. It contains a 8051 8-bit CPU core, 256 bytes of
RAM used as working RAM and stack area, 32k bytes of OTP ROM, 13-channel 8 bit PWM D/A
converter, 2-channel A/D converters for key detection saving I/O pins, internal H. sync and V. sync
signals processor providing mode detection, and an I2C bus interface. When H/V sync through D-Sub
signal cable enter pin 41 and pin 42, the CPU performs frequency / polarity detection and calculate and
send to H/V sync OUT. Then CPU reads the data from I703 and transfer to device 4841 and some DAC
in CPU, above operation takes about 500 ms.
2. There allowed 10 factory preset modes and 8 user modes. There are 15 functions, Contrast, Brightness,
H. Size, H. Position, V. Size, V. Position, Pincushion, Trapezoid, Rotation, H. Moire, V Moire, Pincushion
Balance, Parallel, Top Corner and Bottom Corner, all controlled by OSD icon which can be adjusted by
user.
3. The pin 27 and pin 28 are used for ATE function. When CPU receives C6 as slave address, it will operate
in ATE mode which is used for auto-alignment. After alignment the data will be stored in I703.
4. The user control parameters are selected by OSD icons, through two function keys and flywheel knob,
keys, they are detected by sensing the voltage through R710, R740, R741, R743, R716, R717 to pin 25, 26
and 15 of I701.

Operation Theory Page 11
VM78F
3-3 Deflection Section
1. I2C -- autosync deflection controller is TDA4841.
2. The TDA4841 is a high performance and efficient solution for autosync monitors. All functions are
controllable by I2C bus. SDA and SCL signals coming from microprocessor feed to pin 19 and pin 18 to
control all functions.
3-3-1 Horizontal Section
1. The oscillator is driven by the currents in R419 and R420. The minimum oscillator frequency is determined
by R419 and the maximum frequency is determined by R420.
2. Horizontal sync goes into pin 15 through R318. And horizontal flyback pulse goes into pin 1 through R401
and bypass filter C403 from pin 5 of FBT and R496 for HFLB loop.
3. Horizontal driver (pin8) O/P to Q401 via C410.
3-3-2 Vertical Section
1. Vertical sync goes into pin 14 through R317.
2. The free running frequency is determined by R301 and C301.
3-3-3 Vertical O/P section
1. The differential output currents from pin 13 of Vout1 and pin 12 of Vout2 can be directly coupled to the
vertical deflection booster pin 7 and pin 6 of TDA4863.
2. The TDA4863 has two output stages which are current driven in opposite phase and operate in combination
with the deflection coil in a full bridge configuration.
3. This IC is powered by two sets of positive voltage and one set of negative voltage. (+11.7V at pin 1, -11V
at pin 4, +40V at pin 2).
3-3-4 E-W/Trapezoid and H. Width Controls
1. The horizontal O/P stage uses diode modulator D419, D433, C411, C412, L409 and C418 for East-West
(Pincushion) Trapezoid and H. width controls.
2. The scan current is determined by B+ minus Vm ( the voltage of C418) values and the pincushion control
is accomplished by Darlington pair Q418 and Q419 by coupling a parabola waveform from pin 11 of
TDA4841. The H. width / corner and trapezoid correction are also accomplished by this pin 11. The DC
level controls H. size. The AC level is combined with side pin and trapezoid corners functions.
3-3-5 X-Ray Protection
1. To avoid X-ray hazard, a DC voltage generated at pin 4 of FBT and rectified by D408, C432 and divided
by R403, R404 and R405 come into pin 2 of TDA4841.
2. If this voltage is higher than 6.39 V, then TDA4841 will be activated to float HUNLOCK (pin17), H.
DRV( pin 8), B DRV (pin 6), VOUT1 (pin 12), VOUT2 (pin13). After that all deflection circuit stop
working.

Page 12 Operation Theory
VM78F
3-3-6 G1, Blanking and Brightness
1. The vertical blanking signal comes from pin 16 of TDA4841. This pulse through Q405 amplified and
converted into negative pulse and sent to G1 for vertical blanking.
2. In protection mode or an out-of- range situation HUNLOCK will send 5 V pulse to cutoff Q407, then G1
will go down to -150V. During the mode change, Mute acts as same as HUNLOCK’S.
3-3-7 Contrast Section
1. Contrast is controlled by I701 through I2C bus to I501 (LM1267) directly.
2. Beam current is detected through T402 (FBT) pin 7, C429, R449 and detected voltage feeding into Q432,
Q433, R436, R497, R459, C482 to control I501 pin 22 voltage. When I501 pin 22 voltage drops
below 4.1 V, the ABL function will happen.
3-3-8 H/V size breathing compensation
1. Beam current is sensed as above section (3-3-7 item 2) and this voltage routes through R451, R468, C470
then through R437 to I401 pin 31 for H. size compensation.
2. HV voltage is detected through T402(FBT) pin 11. C481, R4F4, R4F8, R4F9, Q428, R4G0, Q431, R4G1,
then through R302 to I401 pin 21 for V. size compensation.
3-3-9 Dynamic focus circuitry
The dynamic focus is applied to improve the corner focus performance, it includes horizontal and vertical
dynamic focus.
1. Horizontal dynamic comes from C413 and is amplified through T403, L405, H-DY, L402, C411, R417,
C450, C448, R435 and feed to FBT dynamic focus pin (T401 pin 12).
2. Vertical dynamic comes from I401 pin 32 through C315, R322, R326, R321, R323, Q301, R324, R325 and
feed to FBT dynamic focus pin.
3-4 Power Supply Section
3-4-1 AC Rectifier
The circuit can accept 90 V to 264 V AC input through D801~D804 bridge diodes and C808 filtering to get
DC 126 V~364 V for power conversion in T802.
3-4-2 Line Filter
It consists of C803, T801, C804, C805, C808, C819, C807, C817 and meets EMI regulation.
3-4-3 Power LED Status
1. The LED has 3 leads with common cathode to emit green and amber color light for different power
saving states. It is controlled by CPU.
2. Normal : Green light
Amber LED is off because CPU pin 30 is 5V and pin 31 is 0V, only green LED is turned on.
3. Off Mode : Amber light
CPU pin 30 is 0V and pin 31 is 5V, then green is off and amber is illuminated.

Operation Theory Page 13
VM78F
3-4-4 Auto Degaussing
When S801 turns on, pin 14 of I701 will send a signal to Q802 and turns on RL801 for degaussing. After 4
seconds, it will turn off RL801 automatically.
3-4-5 PWM Control
1. Start Up
The I801 (5S0765C) gets power from R807, R808, C830 and pin 3 voltage reaches 15 V for starting up.
The I801 starts oscillation at 20 kHz, pin 1 output to drive T802. Switching on, R819 set up an 15 V to
keep I801 working through D809 auxiliary voltage.
2. Regulation
The DC O/P voltage is proportional to the auxiliary voltage, so I801 pin 4 senses the feedback voltage
from the divider D806, R809, C810, VR801, Q803, Q801 and R821 to compare with the built-in 1.5 volts
reference voltage for error amplifier operation. Finally pin 4 can modulate the different duty cycle by
VR801 setting to achieve regulation purpose.
3-4-6 Synchronization
1. Normal Mode
The sync pulse from FBT (31 kHz~86 kHz) via R812, R811 and C815 to pin 5 of I801 to keep I801
synchronized with horizontal sync input frequency.
2. Power Saving Modes: Standby/Suspend
Because there is no pulse from FBT, so the free-run frequency SMPS works at 20 kHz by I801 itself.
3. Override
The horizontal free run frequency is about 63.2 kHz under override condition, SMPS is synchronized to
this frequency.
3-4-7 O.V.P.
If the auxiliary voltage is higher than 25 volts makes pin 3 of I801 is limited to have the OVP activated.
3-4-8 O.P.P.
The excess current of T802 through I801 pin 1, 2, make Vs>1.1V internal of I801, then limite the power.
3-4-9 Step Up Power Supply For FBT
1. The B+ of FBT is proportional to horizontal frequency, that is the higher frequency, the higher voltage.
The basic voltage is 49 volts from T802 pin 10 via L811, D813, C824 and the gate control of Q451 comes
from I401 pin 6 via Q450, Q434, D435 and R4E5. The duty cycle is controlled by I701 pin 33 (PWM pin
Adj.) via R719, C741, R4F6, R4F5, R4F1.
2. The regulation and boost up (from 56 V to 172 V or more, on demand). The H.V. is set at 25 kV (zero
beam) by I301 pin 33 which senses the secondary O/P from FBT. The booster comprises Q451, L410,
L411, D450, C425 and T802 to offer the required B+ for different frequency modes.

Page 14 Operation Theory
VM78F
3-5 Video Amplifier Section
1. RGB signal inputs are terminated by R501, R531 and R561 then pass through the coupling capacitors
C503, C533 and C563 to IC501 LM1267 preamplifier.
2. The amplifier RGB signals (0~3 Vpp) are adjusted by I2C bus, I501 pin 23 is for clamp pulse which comes
from pin 16 of TDA4841 to set up equal clamp level.
3. The video output stages are amplified by I502 (LM2467).
4. The RGB cathodes cut off are adjusted by I503 (LM2479) pin 8, 7, 6, which comes from I501 pin 16, 15,
14 to adjust cut iff voltage level by I2C bus.
5. Under override condition, “NO SIGNAL” will show up on the screen.
3-6 OSD (On Screen Display) Circuit
1. The I504 MTV021-08 is OSD IC. The OSD signals are worked by positive vertical pulse from I701 pin
34 that goes through R720 to I502 pin 10, and positive horizontal pulse from T402 pin 5 goes through R496
to I502 pin 5. CPU I701 pin 13, 12 (I2C bus) transfers information to I502 pin 7, 8.
2. The OSD R. G. B signals and blanking signal are terminated at I502 pin 15, 14, 13, and 12 to I501 pin 1,2,
3 and 4 then the OSD picture appears.

Page 15
Alignments and Adjustments
VM78F
4Alignments and Adjustments
This section of the service manual explains how to make permanent adjustments to the monitor settings.
4-1 General Adjustments
4-1-1 Adjustment Conditions
a) Power Supply
Apply AC 115 V or 220 V
b) Warm-up Time
The monitor must be powered on for 15 minutes before starting any alignment, but requires 30 minutes of
warm-up time for convergence adjustment.
c) Signal Input
1. Video: RGB Analog, 0.7 Vp-p, positive
2. Synchronization: Horizontal and vertical TTL signal, separate, positive or negative
3. All adjustments should be made using a signal of FH = 86kHz, FV = 85 Hz, unless otherwise defined.
4-1-2 Equipment Required
The following equipments are necessary for adjustment procedures:
1. Volt-ohm-A meter (Sanwa FD-750C or equivalent)
2. 30 kV high voltage probe (HP34111A)
3. Oscilloscope (TEK2235 or equivalent)
4. Minolta Color Analyzer II
5. Signal generator (IBM PC with proper display cards or Chroma 2000)
6. Screwdriver
4-1-3 Switching Power Supply and Regulator Adjustment
a. The regulated B+ control has been preset in the factory and needs no adjustment. However, if any repair
is made on the power supply section, the following readjustment procedures are recommended:
1. Allow the monitor to warm-up for about 15 minutes.
2. Apply VGA (1280 x 960 @ 86 kHz/85 Hz) signal to the monitor.
3. Connect a DC voltage meter to TP001 (on the Main board), and adjust VR801 for 11.7 ± 0.1 Vdc
4. If a fuse is broken during adjustment, remember to replace it with the exact same type of fuse.
b. If necessary, follow the following procedures to enter the factory mode.
1. Press both ENTER key simultaneously then power ON.
2. After turn the power off, this monitor will go back to normal mode.

Page16 Alignmentsand Adjustments
VM78F
4-2AlignmentProcedures
4-2-1HighVoltageAdjustment
CONDITION
Press 1and 2keysimultaneouslywhenswitching thepower“On”.
Displayimage:Novideo(86kHzMode)
PROCEDURE
ConnectDCmetertoTP002 and adjustHV (icon)
ObtainaDCvoltageof-152 ±0.2VDC(Sampo FBT)forCPTCRTM41AGE93X76 (TCO).
4-2-2Screenand WhiteBalance Adjustment
CONDITION
Press 1and 2keysimultaneouslywhenswitching thepower“On”.
Displayimage:Novideo(86kHZMode)
PROCEDURE
1Rastercolorsetting
1-a.SetBrightness max.to77 (OSDcursor) and 563±5atG2.
1-bAdjustRand Bcutoff tomin.
1-cAdjustGcutoff toabout0.45FL
1-dAdjustBcutoff togety=283 ±5,Rcutoff togetx=298±5and Y=0.65 ±0.05FL.
1-eAdjustBrightnesscutoff toraster0.01-0.02FL.
CONDITION
Displayimage:50mmx50 mm whiteblockpattern
PROCEDURE
2 65000Kcolortemperaturesetting
2-a.SetBrightness tocutoffandContrasttomaximum.
2-bMovecursoronOSDtochoosecolortemperatureicon.
2-c.Withgreenblockpattern,adjustGgaintogetYabout32FL.
2-dAdjustR.B.gaintogetx=313 ±5,y=329 ±5;and Y=43 ±0.5FL
3 93000Kcolortemperaturesetting
3-a.SetBrightness tocutoffandContrasttomaximum.
3-bMovecursoronOSDtochoosecolortemperatureicon.
3-c.Withgreenblockpattern,adjustGgaintogetYabout32FL.
3-dAdjustR.B.gaintogetx=283±5,y=298±5;and Y=43±0.5FL

Page 17
Alignments and Adjustments
VM78F
4Full white ABL setting
CONDITION
Display image : full white pattern
4-a Set Brightness to cutoff and Contrast to maximum.
4-b. Adjust ABL to Y=29FL ± 1FL.
4-c. Check the white balance at 5FL and 30FL.
4-d. Repeat all the procedures in 4-2-2 section until the best white balance is obtained.
4-2-3 Focus Adjustment
CONDITION
Display image : “me” character pattern (68.68 kHz Mode)
PROCEDURE
1. Set Brightness to cutoff and Contrast to maximum.
2. Adjust focus 1 at T402 (static focus VR) to make vertical line clear.
3. Adjust focus 2 at T402 (static focus VR) to make horizontal line clear.
4. Repeat above procedures to get best focus.
4-2-4 Static Convergence Adjustments
Static convergence involves alignment of the red, blue and green lines in the center area of the display.
Note : The monitor requires 30 minutes of warm-up time for convergence adjustment.
CONDITION
Display image : Crosshatch pattern
Warm-up Time : 30 minutes
PROCEDURE
1. Set Brightness and Contrast to display a well-defined pattern.
2. Ensure the convergence magnet rings are correctly positioned on the CRT.
Figure 5-1. Convergence Magnets on the CRT
+
87 65 4 3 2
10
1
11
CRT
FRONT
P
9
1) Setup Bolt 2) Bow Magnet 3) Band 4) 2-Pole Magnet
5) Spacer 7) Spacer
9) Holder 6) 4-Pole Magnet 8) 6-Pole Magnet 11) Tabs10) Band

Page 18 Alignments and Adjustments
VM78F
4-2-5 Degaussing
Degaussing is required when poor color impurity appears on the screen. This monitor uses an automatic
degaussing circuit that is activated when the power is on. The automatic degaussing will be fully functional
again after the monitor has been in operation for 20 minutes.
The degaussing effect is confined to the picture tube since the coils are mounted at the back of the tube.
Should any part of the chassis or cabinet becomes magnetized, it is necessary to degauss the affected area
with a manual degaussing coil.
4-2-6 Manual Degaussing
1. Apply line voltage to the degaussing coil and move it in a rotary motion over the front, sides, and top of the
monitor. The coil should be kept away from the rear of the monitor to avoid damaging the magnetic neck
components.
2. Slowly rotate and move the coil away from the monitor to about 6 feet beyond the point where no effect
on the CRT will be noticeable.
For proper degaussing, it is essential that the field be gradually reduced by moving the coil slowly away from
the monitor. The degaussing coil must never be shut off or disconnected while near the monitor, as this would
introduce a strong field instead of canceling the effect of the stray fields.
3. Rotate the individual rings of 4-pole convergence magnets by changing the spacing between the 2 tabs to
converge the vertical red and blue lines at the center of the screen.
4. Rotate the pair of rings of 4-pole convergence magnets by maintaining spacing between the 2 tabs to
converge the horizontal red and blue lines at the center of the screen.
5. Rotate the individual rings of 6-pole convergence magnets by changing the spacing between the 2 tabs to
converge the vertical red, blue and green lines.
6. Rotate the pair of rings of 6-pole convergence magnets by maintaining spacing between the 2 tabs to
converge the horizontal red, blue and green lines.
7. Repeat the steps from 3~6 until the best convergence is obtained.
Note : The 4-pole magnets and the 6-pole magnets interact, making dot movement complex.
Blue Red
Blue
Red
Red/
Blue Green
Red/
Blue
Green
4-pole magnets
movement
6-pole magnets
movement
Figure 5-2. 4-pole and 6-pole Magnets Movement

Page 19
Troubleshooting
VM78F
Check voltage of
cathode, heater,
Grid 1, Grid 2, etc.
Check I401,
I703, R719, C741,
R4F6, R4F5, R4C4
Check
I801, R807,
R808, Q801,
Q802, ZD802,
VR801
Check D801,
D802, D803,
D804, T801,
R804, F801
Yes
No
Normal
(56 V, 31.5 kHz)
Short Circuit
at load?
Measure
voltage of B+ at
T402 pin 2 on
PWB-MAIN
No Raster
0 V High
(75 V or more)
Check DC
B+ line, Q451,
Q402, T402
Yes
Check voltage
of C808
No
5Troubleshooting
5-1 No Raster