Vibrant VM77S User manual

17-inch Color Monitor
VM77S
Service Manual

VM77S
Service Manual Versions and Revision
Copyright
Copyright 2002 Tatung (UK) Ltd.
All Rights Reserved
This manual may not, in whole or in part, be copied, photo-
copied, reproduced, translated, or converted to any elec-
tronic or machine readable form without prior written per-
mission of Tatung (UK) Ltd.
VM77S Service Manual.
Printed in Taiwan.
No. Version Release Date Revision
1. 1.0 May 17, 2002 Original release

Page 1
VM77S
Table of Contents
1. Precautions .................................................................................................................2
2. Product Specifications ..............................................................................................5
3. Operation Theory.......................................................................................................9
4. Alignments and Adjustments...................................................................................14
5. Troubleshooting........................................................................................................18
6. Recommended Spare Parts List..............................................................................24
7. Block Diagram..........................................................................................................26
8. Exploded Diagrams ........................................................................................ Inserted
9. PCB Diagrams ................................................................................................ Inserted
11. Schematic Diagrams ...................................................................................... Inserted

PrecautionsPage 2
VM77S
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,equivalentto0.2 milliampereAC. 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
VM77S
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 modelPM5530ADT orKIKUSUTOS-8750 voltage testeror equivalent approvedequipment.
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.