THE DREADED LINE OF COINCIDENCE

Exaggerated "line of coincidence"

Problem description
Some people run into a problem which is best described as a horizontal line running from the side of the screen towards the center. Often this line is associated with a particular color and more visible at some resolutions than others. Barco calls this line the "line of coincidence". I guess due to the fact that a particular convergence setting just "happens" to overlap a number of scanlines in the same area ;-). From what i understand the problem is common to virtually all Barco's due to the way they build up the image.

Common cause
Experts agree that this line is almost always caused by an incorrect physical setup. If the projector and screen are not 100% level or parallel, the user will need to "overdrive" the convergence of the projector to get the rasters to overlap properly with this horizontal line as an side-effect.

Common solution
In most cases the line will disappear when you reduce the top and bottom bow or keystone of the raster. In some cases reducing convergence on the raster line opposite to the problem area will get rid of the line or reduce it to become virtually invisible. I recommend checking the physical setup and alignment of your projector and screen. Use a spirit level to make sure both your projector and screen are mounted correctly. Also check if the vertical center of the projector is aligned with the vertical center of the screen.

Before proceeding with the next section, make ABSOLUTELY CERTAIN that you have tried all this.

Exaggerated red tube deflection angle problem

Deflection coil angles
Normally, the deflection coils for each tube are positioned at an angle which causes the rasters for the three tubes to be projected in such a way that the middle horizontal line of each raster (genlocked pattern) is parallel and level with the middle horizontal line of the other rasters and the projector mounting surface and screen.

Checking angles
You can check if your deflection coil angles are okay by resetting convergence to midposition, mounting your projector on a level surface and project the genlocked pattern on a level screen. The middle line for each raster should be exactly level and either overlap or run parallel to the middle lines of the other rasters. In some cases you will find that the angle for one of the tubes is off due to the fact that the yoke has been slightly rotated (maybe a technician bumped into it while replacing a board). If the raster of one tube is rotated in relation to the others you will never be able to get convergence right and keep running into the aforementioned horizontal line in your projected image. In this case, the deflection yoke will need to be readjusted in order to correct the problem.

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