Quantum Data 881, User Manual

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882 Video Test Instrument User Guide (Rev A.35) 617
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, determine the correct physical size of the active video area for the display. This
information usually is given in a display’s specification sheet or service manual. The size
should match the sizes in the format you are 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 end points 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 end points 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 specification. The problem usually can be traced to the improper winding of the
yoke coils. If the problem is not 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.
Method Measure the lengths of the two (2) diagonal lines. Any difference is an indication of
parallelogram distortion. The difference in readings should be within the specifications of
the monitor.
If the difference in the readings is too far beyond specification, the monitor should be
rejected and sent back for repair, rather than trying to magnet a defective yoke.
Test Trapezoid distortion correction
Purpose This image gives you a way to measure trapezoid distortion in your monitor. If the
distortion is not too severe, you may be able to correct it by adding or adjusting magnets
on the yoke.
Method Perform the yoke winding orthogonality check and parallelogram distortion check first to
avoid wasting time on a monitor with a defective yoke.