扫二维码下载作业帮
拍照搜题，秒出答案，一键查看所有搜题记录
下载作业帮安装包
扫二维码下载作业帮
拍照搜题，秒出答案，一键查看所有搜题记录
Adventure is in my blood. And I had been considering how I was going to celebrate my high school graduation. I didn’t just want a small
&&& in the backyard. I started thinking about doing a solo
&&& somewhere out of the ordinary. I took out
&&& and drew the 1,500-mile route along which I would be
&& &from the northernmost point in Norway to the southernmost section of Sweden. When I
&&& my plans with my dad, he
&& &as I thought he would. Because I get my adventurous
&&& from him, he was all for it. I had only been away from my
&& &three days now, but there was an inner
&&& going on inside of me. Part of me was homesick and doubting whether I
&& &could make it. The other part of me was ready to
&&&& &to myself and my family that I could do it by myself. On the road, I met another
&&&&& who was quite a bit older than I was. He had started his journey &&&& &by bike at the southern part of Norway and had just finished. I could tell he had a great sense of
&&&& &. It encouraged me not to
&&&& &. As I listened to my
&&&&& artists on my MP4 player, I pedaled (踩踏板) with my feet. There was
&&&& &around me for miles.
&&&&& , that wasn’t entirely true. There were mosquitoes--- millions of them. My arms were so dotted with
&&&& &that they looked like a topographical map (地形图). But, however
&&&& &it would be, nothing could stop my advance towards the destination. As you know, adventure is in my blood.
A．meeting
C．conversation
D．lecture
B．interview
D．performance
A．instructions
C．magazines
D．newspapers
A．walking
D．running
B．compared
C．prepared
D．changed
A．stories
B．hobbies
D．spirits
A．request
B．activity
D．discussion
A．certainly
B．reasonably
C．usually
C．bicyclist
C．patiently
D．worriedly
B．direction
C．satisfaction
D．balance
<td width="25%
神i射龙151
扫二维码下载作业帮
拍照搜题，秒出答案，一键查看所有搜题记录
小题1:B小题2:C小题3:B小题4:B 小题5:A小题6:C小题7:D小题8:A小题9:C小题10:D小题11:C小题12:C小题13:B小题14:C小题15:D小题16:B小题17:A小题18:C小题19:D小题20:B
为您推荐：
扫描下载二维码Notes on the Troubleshooting and Repair of Computer and Video
Notes on the Troubleshooting and Repair of Computer and Video Monitors
Version 3.22 (5-Dec-09)
Reproduction of this document in whole or in part is permitted
if both of the following conditions are satisfied:
This notice is included in its entirety at the beginning.
There is no charge except to cover the costs of copying.
Table of Contents
Author: Samuel M. Goldwasser
For contact info, please see the
Working inside a CRT-based computer or video monitor, or television set can
be lethal from line-connected and high voltage power supplies as well as
CRT implosion.
Read and follow ALL of the safety guidelines found in
and the section "SAFETY", below.
If in doubt about your
abilities or experience, leave repair and internal adjustments to a
professional.
We will not be responsible for damage to equipment, your ego, county wide
power outages, spontaneously generated mini (or larger) black holes, planetary
disruptions, or personal injury or worse that may result from the use of this
Introduction
In the early days of small computers, a 110 baud teletype with a personal
paper tape reader was the 'preferred' input-output device (meaning that
this was a great improvement over punched cards and having to deal with
the bozos in the computer room.
Small here, also meant something that
would comfortably fit into a couple of 6 foot electronics racks!)
The earliest personal computers didn't come with a display - you connected
them to the family TV.
You and your kids shared the single TV and the
Flintstones often won out.
The Commodore 64 would never have been as
successful as it was if an expensive monitor were required rather than
an option.
However, as computer performance improved, it quickly became clear that
a dedicated display was essential.
Even for simple text, a TV can only
display 40 characters across the screen with any degree of clarity.
When the IBM PC was introduced, it came with a nice 80x25 green monochrome
text display.
It was bright, crisp, and stable.
Mono graphics (MGA or MDA)
was added at 720x350, CGA at a range of resolutions from 160x200 to 640x200
at 2 to 16 colors, and EGA extended this up to a spectacular resolution of
This was really fine until the introduction of Windows (well, at
least once Windows stayed up long enough for you to care).
All of these displays used digital video - TTL signals which coded for a
specific discrete number of possible colors and intensities.
Both the video
adapter and the monitor were limited to 2, 4, 16, or a whopping 64 colors
depending on the graphics standard.
The video signals were logic bits - 0s
With the introduction of the VGA standard, personal computer graphics
became 'real'.
VGA and its successors - PGA, XGA, and all of the SVGA
(non) standards use analog video - each of the R, G, and B signals is
a continuous voltage which can represent a continuous range of intensities
for each color.
In principle, an analog monitor is capable of an unlimited
number of possible colors and intensities.
(In practice, unavoidable noise
and limitations of the CRT restricts the actual number to order of 64-256
distinguishable intensities for each channel.)
Note that analog video was only new to the PC world.
TVs and other video
equipment, workstations, and image analysis systems had utilized analog
signals for many years prior to the PC's 'discovery' of this approach.
all fairness, both the display adapter and monitor are more expensive so
it is not surprising that early PCs did not use analog video.
Most of the information in this document applies to color computer video
monitors and TV studio monitors as well as the display portions of television
Black and white, gray scale, and monochrome monitors use a subset
of the circuitry (and generally at lower power levels) in color monitors so
much of it applies to these as well.
For most descriptions of symptoms, testing, diagnosis, and repair, an
auto-scan PC SVGA monitor is assumed.
For a fixed frequency workstation
monitor, studio video monitor, or closed circuit TV monitor, only a subset
of the possible faults and procedures will apply.
Note: we use the term 'auto-scan' to describe a monitor which accepts a wide
(and possibly continuous) range of scan rates.
Usually, this refers mostly
to the horizontal frequency as the vertical refresh rate is quite flexible on
many monitors of all types.
Fixed scan or fixed frequency monitors are
designed to work with a single scan rate (though a 5% or so variation may
actually be accepted).
Multi-scan monitors sync at two or more distinct
scan rates.
While not very common anymore, multi-scan monitors may still
be found in some specific applications.
See the documentss:
for additional
useful pointers.
Since a monitor must perform a subset of the functions
of a TV, many of the problems and solutions are similar.
For power related
problems the info on SMPSs may be useful as well.
If you are considering
purchasing a monitor or have one that you would like to evaluate, see
the companion document: .
Note: throughout this document, we use the term 'raster' to refer to the
entire extent of the scanned portion of the screen and the terms 'picture',
'image'. or 'display', to refer to the actual presentation content.
Monitors designed for PCs, workstations, and studio video have many
characteristics in common.
Modern computer monitors share many
similarities with TVs but the auto-scan and high scan rate deflection
circuitry and more sophisticated power supplies complicates their servicing.
Currently, most inexpensive computer monitors are still based on the Cathode
Ray Tube (CRT) as the display device.
However, handheld equipment,
laptop computers, and the screens inside video projectors now use flat
panel technology, mostly Liquid Crystal Displays - LCDs.
a lot less bulky than CRTs, use less power, and have better geometry - but
suffer from certain flaws.
As the price of LCD (and other technology) flat
screen technology decreases, such monitors will become dominant for desktop
computers as well and CRT based monitors will eventually go the way of
dinosaurs, core memory, and long playing records that dominated their
respective industries for decades but eventually yielded to fundamentally new
technology. :)
However, there are still problems with (low cost, at least) LCD monitors.
First, the picture quality in terms of gray scale and color is generally
inferior to a decent analog monitor.
The number of distinct shades of
gray or distinct colors is a lot more limited.
They are generally not as
responsive as CRTs when it comes to real-time video which is becoming
increasingly important with multimedia computers.
This is partly due to
the response of the LCD material itself but also a result of the scan
conversion that's needed for non-native resolution formats.
Brightness
is generally not as good as a decent CRT display.
And last but not least,
the cost is still somewhat higher due both to the increased complexity of flat
panel technology and lower production volumes (though this is certainly
increasing dramatically).
It is really hard to beat the simplicity of the
shadow mask CRT.
The really bad news from the perspective of repair is that they generally
cannot be repaired outside of a manufacturer authorized service center and
the way they do the repair most likely will be to swap the entire LCD/driver
panel, if not the entire monitor.
Only repair of the most simple problems
like obvious bad connections, a bad cable, a bad backlight lamp, or a failure
of the power supply or backlight inverter, can realistically be accomplished
without fancy specialized test equipment and facilities.
Access to the
backlight lamps might substantial disassembly.
Buying a broken LCD monitor to repair may have better odds than the
State Lottery, but probably not by much.
Where one or more columns or
rows or an entire half screen are not displaying properly, I wouldn't
consider it unless nearly totally free, hoping for a miracle, and even then it
might not be worth it.
Loose connectors and solder joints are possible,
though not nearly as common as with CRT monitors.
Also a note to those with less than perfect vision: If you tend to view your
monitor from less than 10 to 15 inches, you may be disappointed, or at least
have a hard time getting used to LCD monitors.
The appearance of a CRT
display is nearly independent of viewing angle.
But for an LCD display,
this is not the case.
Only the central part of your field of vision will have
the proper brightness, contrast, and color rendition.
the curser isn't within this central area, it will be harder to locate than
In short, don't just depend on the hype.
An LCD with a slightly
lower contrast ratio and lower price may have a substantially wider viewing
angle and better match to your needs than a top-of-the-line model.
drive multiple LCD monitors before committing to one!
Nonetheless, a variety of technologies are currently competing for use in
the flat panel displays of the future.
Among these are advanced LCD,
plasma discharge, and field emission displays.
Only time will tell which, if
any survives to become **the** picture-on-the-wall or notepad display - at
reasonable cost.
Projection displays, on the other hand, can take advantage of a novel
development in integrated micromachining - the Texas Instruments Inc.
Digital Micromirror Device (DMD).
This is basically
an integrated circuit with a tiltable micromirror for each pixel fabricated
on top of a static memory - RAM - cell.
DMD technology would
permit nearly any size projection display to be produced and would
therefore be applicable to HDTV as well as PCs.
Since it is a reflective
device, the light source can be as bright as needed.
This technology is
already appearing in commercial high performance computer projectors and
is competing for use in totally digital movie theaters to replace the film
projector, but to my knowledge is not in any consumer TV sets - yet.
As noted, the plasma panel flat screen display has been around for several
years in high-end TVs, typically in the 42 inch diagonal range.
they are very expensive ($5,000 to $15,000 as of Winter, 2003), and their
life expectancy may be limited due to the gradual degradation of the active
pixel cells - which occurs faster than for a CRT.
The physical resolution
is also probably still too low to really justify the large screen size for
computer displays.
However, there is little doubt that this or a similar
technology will eventually replace the direct view CRT and 3-tube projection
TVs in the mid to large screen sizes in the not too distant future.
what extent it is used for computer monitors is still unclear.
The remainder of this document concentrates on CRT based computer and video
monitors since these still dominate the market and realistically, they are
the only type where there is a good chance of repair without access to
specialized test equipment and parts.
I wouldn't recommend any sort of
attempt at repair of flat screen TVs or monitors - no matter what the size -
beyond checking for bad connections, dead power supplies, or other obvious
The chance of success is vanishingly small and it's very likely
that even with great care, damage could occur to the panels or circuitry.
The following describe the capabilities which characterize a display:
Resolution - the number of resolvable pixels on each line and the
number of scanning lines.
Bandwidth of the video source, cable, and
monitor video amplifiers as well as CRT focus spot size are all critical.
However, maximum resolution on a color CRT is limited by the dot/slot/line
pitch of the CRT shadow/slot mask or aperture grille.
Refresh rate - the number of complete images 'painted' on the screen
each second.
Non-interlaced or progressive scanning posts the entire
frame during each sweep from top to bottom.
Interlaced scanning posts
1/2 of the frame called a field - first the even field and then the
odd field.
This interleaving reduces the apparent flicker for a given
display bandwidth when displaying smooth imagery such as for TV.
usually not acceptable for computer graphics, however, as thin horizontal
lines tend to flicker at 1/2 the vertical scan rate.
Refresh rate is the
predominant factor that affects the flicker of the display though the
persistence of the CRT phosphors are also a consideration.
Long persistence
phosphors decrease flicker at the expense of smearing when the picture
changes or moves.
Vertical scan rate is equal to the refresh rate for
non-interlaced monitors but is the twice the refresh rate for interlaced
monitors (1 frame equals 2 fields).
Non-interlaced vertical refresh rates
of 70-75 Hz are considered desirable for computer displays.
Television
uses 25 or 30 Hz (frame rate) interlaced scanning in most countries.
Horizontal scan rate - the frequency at which the electron beam(s) move
across the screen.
The horizontal scan rate is often the limiting factor
in supporting high refresh rate high resolution displays.
It is what may
cause failure if scan rate speed limits are exceeded due to the component
stress levels in high performance deflection systems.
Color or monochrome - a color monitor has a CRT with three electron
guns each associated with a primary color - red, green, or blue.
Nearly all visible colors can be created from a mix of primaries
with suitable spectral characteristics using this additive color
A monochrome monitor has a CRT with a single electron gun.
the actual color of the display may be white, amber, green, or whatever
single color is desired as determined by the phosphor of the CRT selected.
Digital or analog signal - a digital input can only assume a discrete
number of states depending on how many bits are provided.
A single bit
input can only produce two levels - usually black or white (or amber,
green, etc.).
Four bit EGA can display up to 16 colors (with a color
monitor) or 16 shades of gray (with a monochrome monitor).
Analog inputs allow for a theoretically unlimited number of possible gray
levels or colors.
However, the actual storage and digital-to-analog
convertors in any display adapter or frame store and/or unavoidable
noise and other characteristics of the CRT - and ultimately, limitations
in the psychovisual eye-brain system will limit this to a practical
maximum of 64-256 discernible levels for a gray scale display or for
each color channel.
However, very high performance digital video sources may have RAMDACs (D/A
convertors with video lookup tables) of up to 10 or more bits of intensity
resolution.
While it is not possible to perceive this many distinct gray
levels or colors (per color channel), this does permit more accurate tone
scale ('gamma') correction to be applied (via a lookup table in the RAMDAC)
to compensate for the unavoidable non-linearity of the CRT phosphor
response curve or to match specific photometric requirements.
Monitors can be classified into three general categories:
Studio video monitors - Fixed scanning rate for the TV standards
in the country in which they are used.
High quality, often high
cost, utilitarian case (read: ugly), underscan option.
closed circuit TV monitors fall into the class.
Input is usually
composite (i.e., NTSC or PAL) although RGB types are available.
Fixed frequency RGB - High resolution, fixed scan rate.
High quality,
high cost, very stable display.
Inputs are analog RGB using either
separate BNC connectors or a 13W3 (Sun) connector.
These often have
multiple sync options.
The BNC variety permit multiple monitors to
be driven off of the same source by daisychaining.
Generally used
underscanned for computer workstation (e.g., X-windows) applications
so that entire frame buffer is visible.
There are also fixed frequency
monochrome monitors which may be digital or analog input using a BNC,
13W3, or special connector.
Multi-scan or auto-scan - Support multiple resolutions and scan rates
or multiple ranges of resolutions and scan rates.
The quality and
cost of these monitors ranges all over the map.
While cost is not
a strict measure of picture quality and reliability, there is a
strong correlation.
Input is most often analog RGB but some older
monitors of this type (e.g., Mitsubishi AUM1381) support a variety
of digital (TTL) modes as well.
A full complement of user controls
permits adjustment of brightness, contrast, position, size, etc. to
Circuitry in the monitor identifies the video scan rate
automatically and sets up the appropriate circuitry.
sophisticated (and expensive) designs, the monitor automatically
sets the appropriate parameters for user preferences from memory as well.
The DB15 high density VGA connector is most common though BNCs may be
used or may be present as an auxiliary (and better quality) input.
Thank IBM.
Since the PC has evolved over a period of 15 years, display
adapters have changed and improved a number of times.
With an open system,
vendors with more vision (and willing to take more risks) than IBM were
continuously coming up with improved higher resolution display adapters.
With workstations and the Apple MacIntosh, the primary vendor can control
most aspects of the hardware and software of the computer system.
New improved hardware adapters were being introduced regularly
which were not following any standards for the high resolution modes (but
attempted to be backward compatible with the original VGA as well as EGA
and CGA (at least in terms of software).)
Vast numbers of programs were
written that were designed to directly control the CGA, EGA, and VGA
Adapter cards could be designed to emulate these older
modes on a fixed frequency high resolution monitor (and these exist to
permit high quality fixed scan rate workstation monitors to be used on PCs)
However, these would be (and are) much more expensive than basic display
adapters that simply switch scan rates based on mode.
Thus, auto-scan
monitors evolved to accommodate the multiple resolutions that different
programs required.
Note: The generic term 'auto-scan' is used to refer to a monitor which
automatically senses the input video scan rate and selects the appropriate
horizontal and vertical deflection circuitry and power supply voltages to
display this video.
Multi-scan monitors, while simpler than true auto-scan
monitors, will still have much of the same scan rate detection and selection
circuitry.
Manufacturers use various buzz words to describe their versions
of these monitors including 'multisync', 'autosync','panasync', 'omnisync',
as well as 'autoscan' and 'multiscan'.
Ultimately, the fixed scan rate monitor may reappear for PCs.
one simple fact: it is becoming cheaper to design and manufacture complex
digital processing hardware than to produce the reliable high quality
analog and power electronics needed for an auto-scan monitor.
being done in the specialty market now.
Eventually, the development
of accelerated chipsets for graphics mode emulation may be forced by
the increasing popularity of flat panel displays - which are basically
similar to fixed scan rate monitors in terms of their interfacing
requirements.
There are two aspects of monitor design that can be described in terms
of analog or digital characteristics:
The video inputs.
Early PC monitors, video display terminal
monitors, and mono workstation monitors use digital input signals
which are usually TTL but some very high resolution monitors may
use ECL instead.
The monitor control and user interface.
Originally, monitors all
used knobs - sometimes quite a number of them - to control all
functions like brightness, contrast, position, size, linearity,
pincushion, convergence, etc.
However, as the costs of digital
circuitry came down - and the need to remember settings for multiple
scan rates and resolutions arose, digital - microprocessor
control - became an attractive alternative in terms of design,
manufacturing costs, and user convenience.
Now, most better quality
monitors use digital controls - buttons and menus - for almost all
adjustments except possibly brightness and contrast where knobs are
still more convenient.
Since monitors with digital signal inputs are almost extinct today except for
specialized applications, it is usually safe to assume that 'digital' monitor
refers to the user interface and microprocessor control.
And, except perhaps
for the very cheapest monitors, all now have digital controls.
Whether a monitor runs interlaced or non-interlaced is almost always
strictly a function of the video source timing.
The vertical sync
pulse is offset an amount equal to 1/2 the line time on alternate fields
(vertical scans - two fields make up a frame when interlaced scanning is
Generally, a monitor that runs at a given resolution non-interlaced can run
interlaced at a resolution with the same number of pixels per line but twice
the number of lines vertically at roughly the same horizontal and vertical
scan rates and video bandwidth (but half the frame rate).
Alternatively, it may be possible to increase the resolution in both
directions while keeping the horizontal scan rate the same thus permitting a
monitor to display the next larger size format.
However, in this case, the
video bandwidth will increase.
Here are a couple of examples:
A monitor that will run 640x240 at 60 frames per second non-interlaced will
run 640x480 at 30 frames per second interlaced.
This would permit a monitor
with a horizontal scan rate of 15.7 kHz (NTSC TV compatible) to display VGA
resolution images - though they will likely flicker since the 30 Hz is way
too low for most graphics.
A resolution of
at 50 frames per second interlaced requires
roughly the same horizontal scan rate (about 42 kHz) as 800x600 at 66 frames
per second non-interlaced.
The flicker may be acceptable in this case being
at 50 Hz for the worst case of single horizontal lines as the high 100 Hz
vertical scan rate will reduce flicker otherwise.
Whether the image is usable at the higher resolution of course depends on many
other factors (in addition to flicker) including the dot pitch of the CRT and
video bandwidth of the video card and monitor video amplifiers, as well as
cable quality and termination.
The ultimate perceived quality of your display is influenced by many aspects
of the total video source/computer-cable-monitor system.
Among them are:
Resolution of the video source.
For a computer display, this is determined
by the number of pixels on each visible scan line and the number of visible
scan lines on the entire picture.
The pitch of the shadow mask or aperture grille of the CRT.
The smallest
color element on the face of the CRT is determined by the spacing of the
groups of R, G, and B colors phosphors.
The actual conversion from
dot or line pitch to resolution differs slightly among dot or slot mask
and aperture grille CRTs but in general, the finer, the better - and
more expensive.
Typical television CRTs are rather coarse - .75 mm might be a reasonable
specification for a 20 inch set.
High resolution computer monitors
may have dot pitches as small as .22 mm for a similar size screen.
A rough indication of the maximum possible resolution of the CRT can be
found by determining how many complete phosphor dot groups can fit across
the visible part of the screen.
Running at too high a resolution for a given CRT may result in Moire - an
interference pattern that will manifest itself as contour lines in smooth
bright areas of the picture.
However, many factors influence to what
extent this may be a problem.
See the section:
Bandwidth of the video source or display card - use of high performance
video amplifiers or digital to analog convertors.
Signal quality of the video source or display card - properly designed
circuitry with adequate power supply filtering and high quality components.
High quality cables with correct termination and of minimal acceptable
length without extensions or switch boxes unless designed specifically
for high bandwidth video.
Sharpness of focus - even if the CRT dot pitch is very fine, a fuzzy
scanning beam will result in a poor quality picture.
Stability of the monitor electronics - well regulated power supplies
and low noise shielded electronics contribute to a rock solid image.
The following are only partly dependent on the monitor's design:
Anti-glare treatment of screen and ambient lighting conditions - No matter
how good are the monitor's electronics, the display can still be washed out
and difficult or tiring to view if there is annoying glare or reflections.
The lighting and location are probably more important than how the screen
itself is designed to minimize glare.
Electromagnetic interference - Proximity to sources of magnetic fields and
power line noise can degrade the performance of any monitor, no matter how
well shielded it might be.
WARNING: No monitor is perfect.
Running comprehensive tests on your
monitor or one you are considering may make you aware of deficiencies you
never realized were even possible.
You may never be happy with any monitor
for the rest of your life!
Note: The intent of these tests is **not** to evaluate or calibrate a monitor
for photometric accuracy.
Rather they are for functional testing of the
monitor's performance.
Obviously, the ideal situation is to be able to perform these sorts of
tests before purchase.
With a small customer oriented store, this may
be possible.
However, the best that can be done when ordering by mail
is to examine a similar model in a store for gross characteristics and
then do a thorough test when your monitor arrives.
The following should
be evaluated:
Screen size and general appearance.
Brightness and screen uniformity, purity and color saturation.
Stability.
Convergence.
Edge geometry.
Linearity.
Size and position control range.
Ghosting or trailing streaks.
Sharpness.
Scan rate switching.
Acoustic noise.
The companion document:
provides detailed procedures for the evaluation of each
of these criteria.
CAUTION: Since there is no risk free way of evaluating the actual scan
rate limits of a monitor, this is not an objective of these tests.
is assumed that the specifications of both the video source/card and the
monitor are known and that supported scan rates are not exceeded.
monitors will operate perfectly happily at well beyond the specified range,
will shut down without damage, or will display an error message.
Others will
simply blow up instantly and require expensive repairs.
Unlike PC system boards where any disasters are likely to only affect
your pocketbook, monitors can be very dangerous.
Read, understand, and
follow the set of safety guidelines provided later in this document
whenever working on TVs, monitors, or other similar high voltage equipment.
If you do go inside, beware: line voltage (on large caps) and high voltage
(on CRT) for long after the plug is pulled.
There is the added danger of
CRT implosion for carelessly dropped tools and often sharp sheetmetal
shields which can injure if you should have a reflex reaction upon touching
something you should not touch.
In inside of a TV or monitor is no place
for the careless or naive.
Having said that, a basic knowledge of how a monitor works and what can
go wrong can be of great value even if you do not attempt the repair yourself.
It will enable you to intelligently deal with the service technician.
will be more likely to be able to recognize if you are being taken for a ride
by a dishonest or just plain incompetent repair center.
For example, a
faulty picture tube CANNOT be the cause of a color monitor only displaying
in black-and-white (this is probably a software or compatibility problem).
The majority of consumers - and computer professionals - may not know even
this simple fact.
This document will provide you with the knowledge to deal with a large
percentage of the problems you are likely to encounter with your monitors.
It will enable you to diagnose problems and in many cases, correct them
With minor exceptions, specific manufacturers and models
will not be covered as there are so many variations that such a treatment would
require a huge and very detailed text.
Rather, the most common problems
will be addressed and enough basic principles of operation will be provided
to enable you to narrow the problem down and likely determine a course of
action for repair.
In many cases, you will be able to do what is required
for a fraction of the cost that would be charged by a repair center.
Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair.
It will also be easier to do
further research using a repair text such as the ones listed at the end of
this document.
In any case, you will have the satisfaction of knowing you
did as much as you could before taking it in for professional repair.
With your new-found knowledge, you will have the upper hand and will not
easily be snowed by a dishonest or incompetent technician.
The following probably account for 95% or more of the common monitor ailments:
Intermittent changes in color, brightness, size, or position - bad
connections inside the monitor or at the cable connection to the computer
or or video source.
Ghosts, shadows, or streaks adjacent to vertical edges in the picture -
problems with input signal termination including use of cable extensions,
excessively long cables, cheap or improperly made video cables, improper
daisychaining of monitors, or problems in the video source or monitor
circuitry.
Magnetization of CRT causing color blotches or other color or distortion
problems - locate and eliminate sources of magnetic fields if relevant
and degauss the CRT.
Electromagnetic Interference (EMI) - nearby equipment (including and
especially other monitors), power lines, or electrical wiring behind walls,
may produce electromagnetic fields strong enough to cause noticeable
wiggling, rippling, or other effects.
Relocate the monitor or offending
equipment.
Shielding is difficult and expensive.
Wiring transmitted interference - noisy AC power possibly due to other
equipment using electric motors (e.g., vacuum cleaners), lamp dimmers or
motor speed controls (shop tools), fluorescent lamps, and other high power
devices, may result in a variety of effects.
The source is likely local - in
your house - but could be several miles away.
Symptoms might include bars of
noise moving up or down the screen or diagonally.
The effects may be barely
visible as a couple of jiggling scan lines or be broad bars of salt and
pepper noise, snow, or distorted video.
Plugging the monitor into another
outlet or the use of a line filter may help.
If possible, replace or repair
the offending device.
Monitor not locking on one or more video scan ranges - settings of
video adapter are incorrect.
Use software setup program to set these.
This could also be a fault in the video source or monitor dealing with
the sync signals.
Adjustments needed for background brightness or focus - aging CRT reduces
brightness.
Other components may affect focus.
These are often easy
internal (or sometimes external) adjustments but some manufacturers have
gone to digital setup requiring expensive an adapter (serial cable) to a PC
and their own (expensive and/or unavailable) software.
Dead monitor due to power supply problems - very often the causes are
simple such as bad connections, blown fuse or other component.
If you need to send or take the monitor to a service center, the repair
could easily exceed half the cost of a new monitor.
Service centers
may charge up to $50 or more for providing an initial estimate of repair
costs but this will usually be credited toward the total cost of the repair
(of course, they may just jack this up to compensate for their bench time).
With new monitors going for under $200, the costs of any significant repair
are no longer justifiable unless there is something unique about your monitor.
Some places offer attractive flat rates for repairs involving anything but
the CRT, yoke, and flyback.
Such offers are attractive if the repair center
is reputable.
However, if by mail, you will be stuck with a tough decision
if they find that one of these expensive components is actually bad.
Monitors become obsolete at a somewhat slower rate than most other electronic
equipment.
Therefore, unless you need the higher resolution and scan rates
that newer monitors provide, repairing an older one may make sense as long as
the CRT is in good condition (adequate brightness, no burn marks, good focus).
However, it may just be a good excuse to upgrade.
If you can do the repairs yourself, the equation changes dramatically as
your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free.
The educational aspects may also be
appealing.
You will learn a lot in the process.
Thus, it may make sense
to repair that old clunker for your 2nd PC (or your 3rd or your 4th or....).
Monitors 101
Please refer to
while reading the following description.
A computer or video monitor includes the following functional blocks:
Low voltage power supply (some may also be part of (2).)
Most of the lower
voltages used in the monitor may be derived from the horizontal deflection
circuits, a separate switchmode power supply (SMPS), or a combination of
Rectifier/filter capacitor/regulator from AC line provides the
B+ to the SMPS or horizontal deflection system.
Auto-scan monitors may
have multiple outputs from the low voltage power supply which are
selectively switched or enabled depending on the scan rate, or an power
supply with programmable output voltage for the deflection system.
A common configuration is a pair of SMPSs where one provides all the fixed
voltages and the other is programmable based on scan rate.
Degauss operates off of the line whenever power is turned on (after
having been off for a few minutes) to demagnetize the CRT.
monitors will have a degauss button which activates this circuitry
as well since even rotating the monitor on its tilt-swivel base can
require degauss.
Horizontal deflection.
These circuits provide the waveforms needed to
sweep the electron beam in the CRT across and back at anywhere from
15 kHz to over 100 kHz depending on scan rate and resolution.
horizontal sync pulse from the sync separator or the horizontal sync
input locks the horizontal deflection to the video signal.
monitors have sophisticated circuitry to permit scanning range of
horizontal deflection to be automatically varied over a wide range.
Vertical deflection.
These circuits provide the waveforms needed to
sweep the electron beam in the CRT from top to bottom and back at
anywhere from 50 - 120 or more times per second.
The vertical sync
pulse from the sync separator or vertical sync input locks the vertical
deflection to the video signal.
Auto-scan monitors have additional
circuitry to lock to a wide range of vertical scan rates.
CRT high voltage 'flyback' power supply (also part of (2).)
color CRT requires up to 30 kV for a crisp bright picture.
Rather than
having a totally separate power supply, most monitors derive the high
voltage (as well as many other voltages) from the horizontal deflection
using a special transformer called a 'flyback' or 'Line OutPut Transformer
(LOPT) for those of you on the other side of the lake.
performance monitors use a separate high voltage board or module which is
a self contained high frequency inverter.
Video amplifiers.
These buffer the low level inputs from the computer
or video source.
On monitors with TTL inputs (MGA, CGA, EGA), a resistor
network also combines the intensity and color signals in a kind of poor
man's D/A.
Analog video amplifiers will usually also include DC restore
(black level retention, back porch clamping) circuitry stabilize the
black level on AC coupled video systems.
Video drivers (RGB).
These are almost always located on a little
circuit board plugged directly onto the neck of the CRT.
They boost
the output of the video amplifiers to the hundred volts or so needed
to drive the cathodes (usually) of the CRT.
Sync processor.
This accepts separate, composite, or 'sync-on-green'
signals to control the timing of the horizontal and vertical deflection
Where input is composite rather than separate H and V syncs (as
is used with VGA/SVGA), this circuit extracts the individual sync signals.
For workstation monitors which often have the sync combined with the green
video signals, it needs to separate this as well.
The output of the sync
processor is horizontal and vertical sync pulses to control the deflection
System control.
Most higher quality monitors use a microcontroller
to perform all user interface and control functions from the front panel
(and sometimes even from a remote control).
So called 'digital monitors'
meaning digital controls not digital inputs, use buttons for everything
except possibly user brightness and contrast.
Settings for horizontal
and vertical size and position, pincushion, and color balance for each
scan rate may be stored in non-volatile memory.
It may communicate with
the video card over the serial VESA bus to inform if of its capabilities.
The microprocessor also analyzes the input video timing and selects the
appropriate scan range and components for the detected resolution.
these circuits rarely fail, if they do, debugging can be quite a treat.
Most problems occur in the horizontal deflection and power supply sections.
These run at relatively high power levels and some components run hot.
This results in both wear and tear on the components as well as increased
likelihood of bad connections developing from repeated thermal cycles.
The high voltage section is prone to breakdown and arcing as a result
of hairline cracks, humidity, dirt, etc.
The video circuitry is generally quite reliable.
However, it seems that
even after 15+ years, manufacturers still cannot reliably turn out circuit
boards that are free of bad solder connections or that do not develop them
with time and use.
The books listed in the section:
include additional information on the theory and implementation of the
technology of monitors and TV sets.
Philips/Magnavox used to have a very nice on-line introduction to a variety
of consumer electronics technologies.
Although their site has disappeared -
and even people who work for them have no clue - I have now recovered
several of the articles including those on TVs, VCRs, camcorders, satellite
reception, and connections.
These as well as most or all of the other articles,
as well a glossary and much more, can be also
be accessed via the .
Copy and paste the following URL into the search box:
/electreference/electreference.html
The earliest (Nov 09, 1996) archive seems to be the most complete.
A number of organizations have compiled databases covering thousands of common
problems with VCRs, TVs, computer monitors, and other electronic equipment.
Most charge for their information but a few, accessible via the Internet, are
either free or have a very minimal monthly or per-case fee.
In other cases, a
limited but still useful subset of the for-fee database is freely available.
A tech-tips database is a collection of problems and solutions accumulated by
the organization providing the information or other sources based on actual
repair experiences and case histories.
Since the identical failures often
occur at some point in a large percentage of a given model or product line,
checking out a tech-tips database may quickly identify your problem and
In that case, you can greatly simplify your troubleshooting or at least
confirm a diagnosis before ordering parts.
My only reservation with respect
to tech-tips databases in general - this has nothing to do with any one in
particular - is that symptoms can sometimes be deceiving and a solution that
works in one instance may not apply to your specific problem.
Therefore,
an understanding of the hows and whys of the equipment along with some good
old fashioned testing is highly desirable to minimize the risk of replacing
parts that turn out not to be bad.
The other disadvantage - at least from one point of view - is that you do not
learn much by just following a procedure developed by others.
There is no
explanation of how the original diagnosis was determined or what may have
caused the failure in the first place.
Nor is there likely to be any list
of other components that may have been affected by overstress and may fail
in the future.
Replacing Q701 and C725 may get your equipment going again
but this will not help you to repair a different model in the future.
Please see the document:
for the most up to date compilation of these resources for TVs,
VCRs, computer monitors, and other consumer electronic equipment.
under "Monitor" and "Manuals/Schematics/Repair Guides" for additional links.
CRT Basics
Note: Most of the information on TV and monitor CRT construction, operation,
interference and other problems. has been moved to the document:
The following is just a brief introduction with instructions on degaussing.
All color CRTs utilize a shadow mask or aperture grill a fraction of an inch
(1/2" typical) behind the phosphor screen to direct the electron beams
for the red, green, and blue video signals to the proper phosphor dots.
Since the electron beams for the R, G, and B phosphors originate from
slightly different positions (individual electron guns for each)
and thus arrive at slightly different angles, only the proper phosphors
are excited when the purity is properly adjusted and the necessary
magnetic field free region is maintained inside the CRT.
purity determines that the correct video signal excites the
proper color while convergence determines the geometric
alignment of the 3 colors.
Both are affected by magnetic fields.
Bad purity results in mottled or incorrect colors.
Bad convergence
results in color fringing at edges of characters or graphics.
The shadow mask consists of a thin steel or InVar (a ferrous alloy)
with a fine array of holes - one for each trio of phosphor
dots - positioned about 1/2 inch behind the surface of the phosphor
With some CRTs, the phosphors are arranged in triangular
formations called triads with each of the color dots at the apex
of the triangle.
With many TVs and some monitors, they are
arranged as vertical slots with the phosphors for the 3 colors
next to one another.
An aperture grille, used exclusively in Sony Trinitrons (and now
their clones as well), replaces the shadow mask with an array of finely
tensioned vertical wires.
Along with other characteristics of the
aperture grille approach, this permits a somewhat higher possible
brightness to be achieved and is more immune to other problems like
line induced moire and purity changes due to local heating causing
distortion of the shadow mask.
However, there are some disadvantages of the aperture grille design:
Weight - a heavy support structure must be provided for the tensioned
wires (like a piano frame).
Price (proportional to weight).
Always a cylindrical screen (this may be considered an advantage
depending on your preference.
Visible stabilizing wires which may be objectionable or unacceptable
for certain applications.
(Definitely on 15" and larger sizes, possibly
on smaller ones as well.)
Apparently, there is no known way around the need to keep the fine
wires from vibrating or changing position due to mechanical shock
in high resolution tubes and thus all Trinitron monitors require
1, 2, or 3 stabilizing wires (depending on tube size) across the
screen which can be see as very fine lines on bright images.
people find these wires to be objectionable and for some critical
applications, they may be unacceptable (e.g., medical diagnosis).
Degaussing may be required if there are color purity problems with the
On rare occasions, there may be geometric distortion caused
by magnetic fields as well without color problems.
The CRT can get
magnetized:
if the TV or monitor is moved or even just rotated.
if there has been a lightning strike nearby.
A friend of mine
had a lightning strike near his house which produced all of the
effects of the EMP from a nuclear bomb.
If a permanent magnet was brought near the screen (e.g., kid's
magnet or megawatt stereo speakers).
If some piece of electrical or electronic equipment with unshielded
magnetic fields is in the vicinity of the TV or monitor.
Degaussing should be the first thing attempted whenever color
purity problems are detected.
As noted below, first try the
internal degauss circuits of the TV or monitor by power cycling a few
times (on for a minute, off for at least 20 minutes, on for a minute,
If this does not help or does not completely cure the problem,
then you can try manually degaussing.
Note: Some monitors have a degauss button, and monitors and TVs that are
microprocessor controlled may degauss automatically upon power-on (but may
require pulling the plug to do a hard reset) regardless of the amount of off
However, repeated use of these 'features' in rapid succession may
result in overheating of the degauss coil or other components.
The 20 minutes
off/1 minute on precedure is guaranteed to be safe.
(Some others may degauss
upon power-on as long as the previous degauss was not done within some
predetermined amount of time - they keep track with an internal timer.)
Commercial CRT Degaussers are available from parts distributors
like MCM Electronics and consist of a hundred or so turns of magnet wire
in a 6-12 inch coil.
They include a line cord and momentary switch. You
flip on the switch, and bring the coil to within several inches of the
screen face. Then you slowly draw the center of the coil toward one edge
of the screen and trace the perimeter of the screen face. Then return to
the original position of the coil being flat against the center of the
Next, slowly decrease the field to zero by backing straight up
across the room as you hold the coil. When you are farther than 5 feet
away you can release the line switch.
The key word here is ** slow **.
Go too fast and you will freeze the
instantaneous intensity of the 50/60 Hz AC magnetic field variation
into the ferrous components of the CRT and may make the problem worse.
WARNING: Don't attempt to degauss inside or in the back of the set (near the
This can demagnetize the relatively weak purity and convergence
magnets which may turn a simple repair into a feature length extravaganza!
It looks really cool to do this while the CRT is powered.
The kids will
love the color effects (but then lock your degaussing coil safely away so they
don't try it on every TV and monitor in the house!).
Bulk tape erasers, tape head degaussers, open frame transformers, and the
"butt-end" of a weller soldering gun can be used as CRT demagnetizers but
it just takes a little longer. (Be careful not to scratch the screen
face with anything sharp.
For the Weller, the tip needs to be in place
to get enough magnetic field.) It is imperative to have the CRT running when
using these whimpier approaches, so that you can see where there are
still impurities. Never release the power switch until you're 4 or 5
feet away from the screen or you'll have to start over.
I've never known of anything being damaged by excess manual degaussing
as long as you don't attempt to degauss *inside* or the back of the monitor -
it is possible to demagnetize geometry correction, purity, and static
converence magnets in the process!
However, I would recommend keeping really
powerful bulk tape erasers-turned-degaussers a couple of inches from the CRT.
Another alternative which has been known to work is to place another similar
size monitor face-to-face with the suspect monitor (take care not to bump or
scratch the screens!) and activate degauss function on the working
While not ideal, this may be enough to also degauss the broken
If an AC degaussing coil or substitute is unavailable, I have even done
degaussed with a permanent magnet but this is not recommended since it is more
likely to make the problem worse than better.
However, if the display
is unusable as is, then using a small magnet can do no harm. (Don't use
a 20 pound speaker or magnetron magnet as you may rip the shadow mask right
out of the CRT - well at least distort it beyond repair.
What I have in
mind is something about as powerful as a refrigerator magnet.)
Keep degaussing fields away from magnetic media.
It is a good idea to
avoid degaussing in a room with floppies or back-up tapes.
When removing
media from a room
remember to check desk drawers and manuals for stray
floppies, too.
It is unlikely that you could actually affect magnetic media but better
safe than sorry.
Of the devices mentioned above, only a bulk eraser or
strong permanent magnet are likely to have any effect - and then only when
at extremely close range (direct contact with media container).
All color CRTs include a built-in degaussing coil wrapped around the
perimeter of the CRT face. These are activated each time the CRT is
powered up cold by a 3 terminal thermistor device or other control
circuitry.
This is why it is often suggested that color purity problems
may go away "in a few days".
It isn' it's the number
of cold power ups that causes it.
It takes about 15 minutes of the power
being off for each cool down cycle. These built-in coils with thermal
control are never as effective as external coils.
Note that while the monochrome CRTs used in B/W and projection TVs and mono
monitors don't have anything inside to get magnetized, the chassis or other
cabinet parts of the equipment may still need degaussing.
While this isn't
likely from normal use or even after being moved or reoriented, a powerful
magnet (like that from a large speaker) could leave iron, steel, or other
ferrous parts with enough residual magnetism to cause a noticeable problem.
See the document:
for some additional discussion of degaussing tools,
techniques, treatments for severe magnetization from lightning strikes,
and cautions.
Some monitor manufacturers specifically warn about excessive use of degauss,
most likely as a result of overstressing components in the degauss circuitry
which are designed (cheaply) for only infrequent use.
In particular,
there is often a thermistor that dissipates significant power for the second
or two that the degauss is active.
Also, the large coil around the CRT
is not rated for continuous operation and may overheat.
If one or two activations of the degauss button do not clear up the color
problems, manual degaussing using an external coil may be needed
or the monitor may need internal purity/color adjustments.
Or, you may have
just installed your megawatt stereo speakers next to the monitor!
You should only need to degauss if you see color purity problems
on your CRT.
Otherwise it is unnecessary.
The reasons it only works the
first time is that the degauss timing is controlled by a thermistor
which heats up and cuts off the current.
If you push the button
twice in a row, that thermistor is still hot and so little happens.
One word of clarification:
In order for the degauss operation to be
effective, the AC current in the coil must approach zero before the
circuit cuts out.
The circuit to accomplish this often involves a
thermistor to gradually decrease the current (over a matter of several
seconds), and in better monitors, a relay to totally cut off the current
after a certain delay.
If the current was turned off suddenly, you would
likely be left with a more magnetized CRT.
There are time delay elements
involved which prevent multiple degauss operations in succession.
this is by design or accident, it does prevent the degauss coil - which is
usually grossly undersized for continuous operation - to cool.
These are not a defect - they are a 'feature'.
All Trinitron (or clone) CRTs - tubes that use an aperture grille - require
1, 2, or 3 very fine wires across the screen to stabilize the array of
vertical wires in the aperture grille.
Without these, the display would be
very sensitive to any shock or vibration and result in visible shimmering or
(In fact, even with these stabilizing wires, you can usually see
this shimmering if you whack a Trinitron monitor.)
The lines you see are the
shadows cast by these fine wires.
The number of wires depends on the size of the screen.
Below 15" there
is u between 15" and 21" there are usually 2
above 21" there may be 3 wires.
(Some very small Trinitron CRTs may not
need these but they will be present on most of the sizes of interest here.)
Only you can decide if this deficiency is serious enough to avoid the
use of a Trinitron based monitor.
Some people never get used to the fine
lines but many really like the generally high quality of Trinitron based
displays and eventually totally ignore them.
Monitor Placement and Preventive Maintenance
Proper care of a monitor does not require much.
Following the recommendations
below will assure long life and minimize repairs:
Subdued lighting is preferred for best viewing conditions.
Avoid direct
overhead light falling on the screen or coming from behind the monitor
if possible.
Locate the monitor away from extremes of hot and cold.
Avoid damp or dusty
locations if possible.
(Right you say, keep dreaming!)
This will help
keep your PC happy as well.
Allow adequate ventilation - monitors use a fair amount of power - from
60 watts for a 12 inch monochrome monitor to over 200 W for a 21 inch
high resolution color monitor.
Heat is one major enemy of electronics.
Do not put anything on top of the monitor that might block the ventilation
grill in the rear or top of the cover.
This is the major avenue for
the convection needed to cool internal components.
Do not place two monitors close to one another.
The magnetic fields
may cause either or both to suffer from wiggling or shimmering images.
Likewise, do not place a monitor next to a TV if possible.
Locate loudspeakers and other sources of magnetic fields at least a couple
of feet from the monitor.
This will minimize the possibility of color purity
or geometry problems.
The exception is with respect to good quality shielded
multimedia speakers which are designed to avoid magnetic interference
Other devices which may cause interference include anything with power
transformers including audio equipment, AC or DC wall adapters, and laptop
fluorescent lamps wi and motorized
or heavy duty appliances.
Situate monitors away from power lines - even electric wiring behind
or on the other side of walls - and heavy equipment which may cause
noticeable interference like rippling, wiggling, or swimming of the
Shielding is difficult and expensive.
Make sure all video connections are secure (tighten the thumbscrews)
to minimize the possibility of intermittent or noisy colors.
cables as short as possible.
Do not add extension cables if at all
possible as these almost always result in a reduction in image crispness
and introduce ghosting, smearing, and other termination problems.
If you must add an extension, use proper high quality cable only long
enough to make connections conveniently.
Follow the termination
recommendations elsewhere in this document.
Finally, store magnetic media well away from all electronic equipment
including and especially monitors and loudspeakers.
Heat and magnetic
fields will rapidly turn your diskettes and tapes into so much trash.
operation of the monitor depends on magnetic fields for beam deflection.
Enough said.
Monitors normally are positioned horizontally or via the limits of their tilt
swivel bases out in the open on a table or desktop.
However, for use in
exhibits or for custom installations, it may be desirable to mount a monitor
in a non-standard position and/or inside an enclosure.
(From: Bob Myers (myers@).)
Your mileage may vary, but (and please take the following for what it is, a
very general answer)...
There are basically two pot one is cooling, and the other
is the fact that the monitor has no doubt been set up by the factory assuming
standard magnetic conditions, which probably DIDN'T involve the monitor
tilting at much of an angle.
If you're happy with the image quality when it's
installed in the cabinet, that leaves just the first concern.
THAT one can be
addressed by simply making sure the cabinet provides adequate ventilation (and
preferably adding a fan for a bit of forced-air cooling), and making sure that
the whole installation isn't going to be exposed to high ambient temperatures.
(Most monitors are speced to a 40 deg. C ambient in thei
adding forced-air cooling will usually let you keep that rating in positions
somewhat beyond the normal.)
Under no circumstances should you block the
cabinet's vents, and - depending on the installation - it may be preferable to
remove the rear case parts of the monitor (but NOT the metal covers beneath
the plastic skin) in order to improve air circulation.
Your best bet is to simply contact the service/support people of the monitor
manufacturer, and get their input on the installation.
Failing to get the
manufacturer's blessing on something like this most often voids the warranty,
and can probably lead to some liability problems.
(Note - I'm not a lawyer,
and I'm not about to start playing one on the net.)
Preventive maintenance for a monitor is pretty simple - just keep the case
clean and free of obstructions.
For CRT monitors, clean the screen with a
soft cloth just dampened with water and mild detergent or isopropyl alcohol.
This will avoid damage to normal as well as antireflection coated glass.
NOT use anything so wet that liquid may seep inside of the monitor around
the edge of the CRT.
You could end up with a very expensive repair bill when
the liquid decides to short out the main circuit board lurking just below.
Then dry thoroughly.
Use the CRT sprays sold in computer stores if you
like but again, make sure none can seep inside.
If you have not cleaned
the screen for quite a while, you will be amazed at the amount of black
grime that collects due to the static buildup from the CRT high voltage
There is some dispute as to what cleaners are safe for CRTs with antireflective
coatings (not the etched or frosted variety).
Water, mild detergent, and
isopropyl alcohol should be safe.
Definitely avoid the use of anything with
abrasives for any type of monitor screen.
And some warn against products with
ammonia (which may include Windex, Top-Job, and other popular cleaners), as
this may damage/remove some types of antireflective coatings.
To be doubly
sure, test a small spot in a corner of the screen.
In really dusty situations, periodically vacuuming inside the case and the use
of contact cleaner for the controls might be a good idea but realistically,
you will not do this so don't worry about it.
Note that a drop of oil or other contamination might appear like a defect
(hole) in the AR coating.
Before getting upset, try cleaning the screen.
For LCD TVs, LCD computer monitors, and laptop displays, the cleaning is
particularly critical.
The front surface of these facing the viewer is
generally not made of glass like those in CRT displays, but rather a plastic
layer or film.
Thus, any cleaning method that uses harsh chemicals
can permanently damage the screen, with or without an
anti-reflection coating.
Some glass cleaners, acetone (nail polish
remover), and other strong solvents can attack the plastic very quickly.
By the time you realize there is damage, it may be too late.
And, of course, NEVER use anything even mildly abrasive.
A damp cloth with soap or detergent and water is
safe, as is generally a damp clost with a solution of 70 percent isopropyl
(rubbing) alcohol diluted in the ratio 1:1 with water.
And it is even more essential to avoid allowing any liguid to seep inside
along the edges as this can short out the circuitry, especially the high
voltage back-light driver,which often located behind the trim at the bottom,
and possibly ruin the display entirely, or at least requiring a major repair.
(From: Bob Myers (myers@).)
Windex is perfectly fine for the OCLI HEA co OCLI's
coating is pretty tough and chemical-resistant stuff.
There may be
alternative (er..cheaper) coatings in use which could be damaged by various
commercial cleaners,
(For what it's worth, OCLI also sells their own brand of
glass cleaner under the name "TFC", for "Thin Film Cleaner".)
I have cleaned monitors of various brands with both Windex and the OCLI-brand
cleaner, with no ill results.
But then, I'm usually pretty sure what sort of
coating I'm dealing with... :-)
Monitor coatings besides the basic "OCLI type"
quarter-wave coatings and their conductive versions developed to address
E-field issues, just about every tube manufacturer has their own brew or three
of antiglare/antistatic coatings.
There are also still SOME tubes that aren't
really coated at all, but instead are using mechanically or chemically etched
faceplates as a cheap "anti-glare" (actually, glare-diffusing) treatment.
In general, look in the user guide/owner's manual and see what your monitor's
manufacturer recommends in the way of cleaning supplies.
(From: Tom Watson ().)
If you are maintaining a site, consider periodic cleaning of the monitors.
Depending on the location, they can accumulate quite a bit of dust.
operation there is a electrostatic charge on the face of the crt (larger
screens have bigger charges) which act as 'dust magnets'. If the operator
smokes (thankfully decreasing), it is even worse.
At one site I helped out
with, most of the operators smoked, and the screens slowly got covered with a
film of both dust and smoke particles.
A little bit of glass cleaner applied
with reasonable caution and the decree of "adjustments" to make the screen
better (these were character monochrome terminals), and lo and behold, "what
an improvement!". Yes, even in my dusty house, the TVs get a coating of
film/goo which needs to be cleaned, and the picture quality (BayWatch viewers
beware) improves quite a bit.
Try this on your home TV to see what comes off,
then show everyone else.
You will be surprised what a little bit of cleaning
(From: Bob Myers (myers@).)
Don' make sure the monitor has adequate ventilation,
and don't operate it more than necessary at high ambient temperatures.
If the monitor is used in particularly dusty environments, it's probably
a good idea to have a qualified service tech open it up every so often
(perhaps once a year, or more often depending on just how dirty it gets)
and clean out the dust.
The usual sorts of common-sense things - don't subject the monitor to
mechanical shock and vibration, clean up spills, etc., promptly, and
And if you're having repeated power-supply problems with your
equipment, it may be time to get suspicious of the quality of your AC
power (are you getting noise on the line, sags, surges, spikes, brownouts,
that sort of thing?).
And most importantly:
Turn the monitor OFF when it's not going to be used for an extended
period (such as overnight, or if you'll be away from your desk for the
afternoon, etc.).
Heat is the enemy of all electronic components, and
screen-savers do NOTHING in this regard.
Many screen-savers don't even
do a particularly good job of going easy on the CRT.
With modern
power-management software, there's really