cut off and drive... what do they do specifically?

[Frankiebonez]

What do the cut off and drive controls on the neck board do?  I'm assuming drive is how much of a certain color there is on a screen.  Cut off I'm unsure of really... I tried searching but nothing really came up that was helpful.

[grantspain]

i refer to these as foreground and background colours

[Frankiebonez]

Alright so cutoff does what specifically?  Add to background colors more or less?  I would just go turn the dials and try it out but I dont wanna mess up anything hehe.

[Rickn]

I will try to give you an expanation that should help, here goes.

Use the term cutoff literaly. In other words if there is no signal ( reg, Green, Blue) the screen would be set so it is black, this is called "cathode Cutoff"

Drive is the amount of drive or amplification given to the video output transistors... technicaly it goes deeper than that, but let's cut to the chase if you want to know how to adjust these controls, here is a generic procedure.

Before we start mark all control positions so you can return to the original setting if need be.

- Preset the cutoff controls to about 1/3 this is a mecahnical setting for a starting point. Determine it by selecting a color, say red and adjust the control full cw then full ccw. The direction where the red in the cakground is weakest is minimum, advance all cutoffs to 1/3.
-Preset the drive controls to 2/3 (use similar process to determine direction).

Ok now we will set cutoff of the picture tube:
- adjsut the user brightness control to maximum and the contast control to maximum. If you can shut off the colors, do so.
- now assuming you know what the flyback transformer is- the bottom control is the G2 or what is also know as screen control. Adjust it so that the raster (raster is the screen without any video image) so that the screen of the picture tube is just black.

Ok now the tube is set at cutoff, I will give you a visual explanation for the rest that will depend what type of signals you have available.

If you were able to turn the colors off, turn them back on and provide a video image that is noramaly white, because the contrast is minimum, this "white image will be dark" if cutoff were perfect it would be "grey".

As it is probably not grey, you will have to adjust the cutoff's (keep in mind that most monitors have 3 cutoff controls) so that this image is white, for example if the screen is magenta (light purple) add green....

Once you are happy with this increase the contrast to get a brighter white image, now you will have to adjsut the drive controls so that the higher white image appears nice and white, not tinted.

Hope this helps, we use various patterns as well as equipment such as colormeters etc to do it in the factory, but it should get you through.

I have not looked for a while but do a websearch for Nolai Test pattern,there used to be a pattern generating software you could download that would help with this and many other adjustments.

Rick Nieman
Nieman Video Displays
Rick@niemandisplays.com
www.niemandisplays.com