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Test Display size correction
Purpose A too-large active video size adjustment on a monitor
may cause information to be lost around the edges
of the screen. A too-small active video size adjustment
may make some displayed information hard to read.
The correct size is needed to obtain the correct aspect
ratio. You need the correct aspect ratio to get round
circles and square squares.
Method First you need to know the correct physical size of
the active video area for the display. This information
usually is given in a display’s spec sheet or service
manual. The size should match the sizes in the format
you’re using. The size setting of the current format
can be checked using the Format test image.
Place a ruler or gauge along the horizontal line of
the image and adjust the monitor's horizontal size
control until the distance between the endpoints
matches the specified value.
Move the ruler or gauge to the vertical line and
adjust your monitor's vertical size control until
the distance between the endpoints matches the
specified value.
Test Parallelogram distortion check
Purpose Parallelogram distortion is very difficult to correct
with magnets because the correction often causes
barrel distortion. Therefore, you should decide
early whether your monitor meets this spec. The
problem usually can be traced to the improper
winding of the yoke coils. If the problem isn’t too
severe, it may be corrected by adding or adjusting
magnets on the yoke. However, if the distortion
is excessive, it may be an indication of a defective
yoke which cannot be corrected with magnets.