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1993-03-12
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CONVERGE - A CRT Testing Program
DESCRIPTION:
CONVERGE is a highly shareware program which is a useful
evaluation tool for testing VGA (and higher) resolution monitors.
CONVERGE will show such anomalies as geometric distortion,
pincushion, misconvergence, and color smearing. Such testing is
extremely valuable in evaluating monitor performance (you will be
amazed at how many high-priced high-rez monitors are mis-
converged!) when purchasing, or to spot potential trouble in an
existing monitor.
DISCUSSION:
Color CRT monitors use 3 separate colors (red, blue and green)
to optically generate the various shades of the color spectrum on
the monitor face. Proper operation requires that each of the
electron guns inside the picture tube be precisely aligned to
it's assigned color phosphor dots on the picture tube face. (If
you look at your monitor face with a magnifying glass, you can
actually see the 3 colors of phosphor dots.) If any of these guns
are mis-aligned, the resulting display can exhibit blurred color,
bad color, or a distorted image.
Besides mis-convergence (the color alignment mentioned above),
monitors are often plagued with raster (scanning) distortion. To
paint the image on the picture tube, the beams from the 3
electron guns are swept across the face of the picture tube in a
particular pattern. The pattern is an extremely fast left-to-
right sweep that is repeated in a downwards fashion. Older CGA
monitors used a very slow sweep rate, and as a result, tended to
flicker. New high-resolution monitors operate at a much faster
rate, so the eye does not perceive any noticeable flicker from
the screen.
If the circuitry inside the monitor is operating improperly, or
if the circuitry is of a cheap design, then certain raster
distortion effects become apparent when using the convergence
grid.
PINCUSHION DISTORTION is a 'bending' of the left and right
edges of the picture on the screen:
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CONVERGE - A CRT Testing Program
This type of distortion is caused by a mis-adjustment in the
horizontal (left-right) deflection circuitry. You can test for
this type of distortion by selecting the convergence grid and
holding a ruler or other straight-edged object up to the monitor
screen. By examining the white vertical bars at both the left and
right edges of the screen, any pincushion distortion should be
clearly seen. Some monitors such as the NEC 3F,4F,5F and 6F
series have an adjustment control to correct this.
KEYSTONE DISTORTION is a trapezoidal shaped pattern. Typically it
appears as an image which is wider at the top of the screen, then
tends to become narrower at the bottom:
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This type of distortion is invariably caused by an inadequate or
malfunctioning power supply in the monitor. Occasionally a weak
flyback transformer will create this symptom as well. The
convergence grid pattern again may be used, only in this case the
top and bottom white lines are measured for length. If there is a
noticeable difference (approximately 1/8" for a 14" monitor),
there is something wrong with the monitor or it's design.
GEOMETRIC DISTORTION refers to a non-symmetrical scanning
pattern. Usually this is evidenced by a distorted corner,
typically in the upper right corner of the screen:
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Geometric distortion comes from an improperly corrected picture
tube. During manufacture, small magnets are placed in certain
locations on the rear portion of the picture tube. Most monitor
manufacturers do a pretty good job of alignment, but occasionally
one slips through. This is particularly true of the Taiwanese
monitors. Again, the convergence grid may be employed to check
for this, as the outer white rectangle should have 90 degree
square corners. Occasionally some types of monitors will exhibit
a 'blooming' effect, most notably in the center of the screen.
This appears as a bulging outwards of the grid squares, much like
that of a balloon surface that is expanding.
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CONVERGE - A CRT Testing Program
COLOR ALIGNMENT (CONVERGENCE) is crucial for a clear, sharp
image, particularly at high resolutions. As mentioned earlier in
this discussion, the three electron guns (red, blue and green)
must align with their respective phosphor dots to produce a
proper image. If this alignment is off, the edges of any graphic
elements will tend to have fuzzy edges, or a slight color shadow.
This is where the convergence grid really shines. The vertical
lines are yellow in color, which requires exact alignment of the
red and green guns. The horizontal lines are magenta, which
requires exact alignment of the red and blue guns. Finally, the
outer rectangle is white, which requires the exact alignment of
all three guns.
Any color mis-convergence will show up as a separation of
color, or the appearance of color shadowing. For example, if the
red and blue guns are off, the horizontal magenta line will tend
to be blue on one side, and red on the other. Occasionally
geometric scan distortion will appear, causing the line to be
perfect at one end, and separate at the other. The author recalls
one instance where a monitor was so bad that the magenta line
actually turned into separate blue and red lines! A similar
situation occurs with the vertical yellow lines, only this time
the colors will be red and green.
Lastly, the overall color balance of the monitor may be
observed with each of the 3 color flood screens. Look for any
blotchy areas or shadows. Blotches are usually caused by a defect
in the phosphor coating. Shadowy patches are usually a result of
improper demagnetization of the shadow mask, and can usually be
cleared up with a thorough degaussing. (Turn the monitor on and
off several times, waiting about 2 to three minutes per cycle.)
The white screen shows the overall color balance and 'color
temperature' of the phosphors. Some monitors tend to have a
'warm' white, leaning a bit towards the red, while others tend to
appear greenish, similar to florescent lamps. This is more of a
personal preference.
For those people who are trained in electronic repair of
televisions and monitors, this program is also a handy tool to
use when fixing monitors. WARNING! - If you are NOT TRAINED to
perform these types of repairs, DO NOT disassemble or take your
monitor apart! If your monitor is exhibiting any of the symptoms
mentioned, please take your monitor to a repair facility! Lethal
electrical current is present inside the monitor, which can cause
serious injury or death!
PROGRAM OPERATION:
The program initially tests to see if a VGA-compatible graphics
adapter is present. If so, then the program will display the
convergence grid. By pressing the space bar, the program will
cycle through each screen indefinitely. To exit the program,
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CONVERGE - A CRT Testing Program
press the ESC key. NOTE: the space bar has no effect if a
particular screen is specified in the command line.
PROGRAM PARAMETERS:
Sytax: CONVERGE [/c] [/b] [/g] [/r] [/w] [?]
? - Echos a brief help text on the screen. No action is
taken.
/c - Displays the convergence grid. Each square is exactly
on a 1:1 pixel aspect ratio. (Each side is exactly the
same number of pixels in length.)
/b - Displays the blue flood screen.
/g - Displays the green flood screen.
/r - Displays the red flood screen.
/w - Displays the white flood screen.
SHAREWARE CONCEPT:
Shareware is a non-conventional approach to software
distribution. Unlike regular commercial programs, shareware
allows a 'try-before-you-buy' approach. In most cases, the
programs are just as bit as good (if not better in some
instances!) as the programs you buy at a computer store.
Shareware ISN'T freeware! In most cases, the software author is
a professional who makes at least part of his or her living on
the registration of the software program. Typically the user is
enticed into registration by added features, free updates, etc.
Shareware depends upon the user to make it work. It's up to
you!
Registration:
This program is 'donate-ware', which is similar in concept to
shareware. The author makes no claims as being a professional
software engineer, rather, the author is a disabled hardware
engineer who enjoys tinkering with programs, and making the
hardware work better.
If you find that this program is useful, and saves you some
time and headaches, the author would appreciate a $5.00 (US)
suggested donation. This amount would include a 'registered' copy
of the program (without the shareware notice), and the eternal
thanks from the author. Considering that the cost of monitors,
this program may make the difference between a wise purchase and
a costly mistake. With that in mind, 5 bucks is a very small
investment! Of course, any amount is appreciated. Oh, please
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CONVERGE - A CRT Testing Program
specify whether you want a 360K, 5-1/4" or 720K, 3-1/2" floppy
when you register.
.....and the address is:
Brent Turner
P.O. Box 3612
Fullerton, CA, 92634-3612
NOTE: Foreign (non-US) users please include a few extra bucks
for the postage! Thanks.
THE LEGAL STUFF:
This software is distributed on an as-is basis. The author has
made reasonable attempts to ascertain it's performance, but
cannot guarantee that it will work in every instance. The author
is not responsible for any damages, or loss of data resulting
from the use of this program.
The shareware version of this program may be freely distributed
as long as all files are included in the package. The registered
version may not be copied or duplicated.
Shareware vendors may distribute this program as long as the
cost per disk does not exceed $5.00. This program may be included
(bundled) with other programs of like nature, so long as the
above cost-per-disk stipulation is met.
The original source code is not available.
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