Quantum Data 802BT - Manual (Page 676)

666 Appendix B Image Reference
specification for the monitor. If it is out of specification, the yoke must be adjusted. Loosen
the hardware that clamps the yoke to the neck of the CRT and rotate the yoke until the line
is horizontal. Tighten the yoke-clamp hardware.
Test Yoke winding orthogonality check
Purpose The horizontal and vertical deflection coils on the yoke should have their axes cross at
exactly 90 degrees. Improper orientation of the windings causes displayed rectangles to
look more like nonorthogonal parallelograms. This type of defect is almost impossible to
correct with adjustments. It is usually easier to replace the defective yoke.
Method First, perform the yoke tilt correction described above. The vertical center line of the image
should be perpendicular to the work surface. If the deviation is beyond specification, the
monitor should be rejected and sent back for repair, rather than trying to magnet a
defective yoke.
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.