Quantum Data 801GC, 801GF, 801GX Owner's And Programmer's Manual page 46

BLU_PIC, GRAY_PIC, GRN_PIC, RED_PIC,
WHT_PIC, Flat, Flat Gray, Flat_B, Flat_G, and
Flat_R — contd.
Method
Test
Purpose
Method
4-8
Chapter 4: Built-In Images
The methods used for adjusting purity on a color
monitor depend on the type of monitor and CRT
you're using (for example; Delta, In-Line or Single
Gun). In most cases, the first step is to degauss
the CRT.
Note – For a Delta Gun CRT, turn on only the Red output. A
solid uniform field of red should be displayed. If the color is
not uniform, adjust the yoke and the Purity Tabs assembly.
If purity cannot be corrected to acceptable limits,
the monitor may not have been properly degaussed
or there may be a defect in the CRT or purity
assembly.
Shadow mask warping
The purity characteristics of your CRT can change
over time if you leave it on with a lot of video
being displayed. This may be due to the CRT's
electron beams striking its shadow mask with
enough energy to cause the mask to heat. This
internal heating may be enough to cause the
shadow mask to warp and give bad purity.
Set the purity image to white and allow the monitor
to run for a few minutes. Any mask warping shows
up as a change in purity. You can use a color
meter to measure the change. The BriteBox pattern
also may be useful for measuring shadow mask
warping.
Model 801GC, 801GF & 801GX¥Rev. X1