Tatung Vibrant VM78F Service Manual

Service Manual

17-inch Color Monitor
VM78F

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

VM78F

1 Precautions

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 X­ray 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, equivalent to 0.2 milliampere AC. 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

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 Hi­Pot & Ground Continuity tests MUST BE performed before the monitor is returned to user.

1-3 Hi-Pot Test

1. Test Equipment
Puncture test model PM5530 ADT or KIKUSU TOS-8750 voltage tester or equivalent approved 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.

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

VM78F

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.

2 Product Specifications

2-1 Specifications

17-inch (15.8-inch Visual image area), sloted mask, 90 degrees

Picture Tube

deflection, dot type black matrix, medium short persistence

phosphor, dark tint, non-glare/ anti-static screen,

0.25 mm(FNSL/T) dot pitch

VM78F

Scanning Frequency

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

Synchronizatin Signals Separate Sync: horizontal/vertical, TTL, positive or negative

Synchronization

Frequencies

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

VGA, Super VGA, 1024x768@60/70/75/85/100 Hz

1280x1024@60/75 Hz

Unlimited Colors

Horizontal : 30 to 86 kHz
Vertical : 50 to 120 Hz

User Controls Power On/Off, Contrast, Brightness, Horizontal Size, Horizontal

Service Controls PWB-1619

Preset Modes 12 (see Table 2-2. Timing Chart)

Environmental

Considerations

Note: Above specifications are subject to change without prior notice.

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

PWB-1620 : power voltage adjust (VR801)

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

2-2 Signal Cable Pin Connections

Table 2-2. Signal Cable Pin Assignment

Pin Signal Pin Signal

1 Red video 9** +5V

2 Green video 10 Digital Ground
3 Blue video 11 Ground
4 Ground 12 SDA
5* NC 13 H-Sync
6 Red ground 14 V-Sync/VCL

VM78F

7 Green ground 15 SCL
8 Blue 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.

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

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 1 1.556 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 + - + - + + + + + + + +

Seperate Sync

Horizontal

C

E

Video

D

Sync

A

B

F

H.Parameters:

A: Period B: Blanking Time
C: Sync Width D:Back Porch
E: Active Time F: Front Porch

Vertical

I

V.Parameters:

G: Period H:Blanking Time
I: Sync Width J: Back Porch
K: Active Time L: Front Porch

K

Video

J

Sync

G

H

L

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)

State LED Color H-Sync V-Sync Power

Consumption

ON Green Pulse Pulse Normal*

OFF Amber No Pulse No Pulse <5 watts

* 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

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.

+/- 500 V +/- 500 V

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 environmen­tal requirement.