Recently, I began working at a small graphics design firm, where I was unluckily given an old 19 or 20 inch monitor (SuperScan Mc 801 RasterOps) which is clearly ailing. It works OK, but for as a graphic designer, it isn't acceptable screen quality.

The problem is that there are horizontal lines radiating from the sides of the monitor into the center. They are stronger at the edges and they are slightly warped, like wrapping around the curvature of the monitor (which has a greater surface curve than newer flat panel CRTs). The lines are pretty faint, but they are disturbing.

No amount of screen control adjustments made a difference.

Before convincing my boss to spring on a brand new graphics- quality monitor, I want to be sure if it is worth fixing or not.

It's definitely out of warranty.

Any advice would be greatly appreciated.

What you are describing is moiré patterns. Some monitors have an adjustment for this, but in your case it may be a power supply problem (dried-out electrolytic capacitors). This is a common problem with this class of monitors.

Does the problem change with different scan rates? Does the problem change with adjustments to height or width?

Dry caps are usually economical to replace, especially if the unit works OK otherwise.

Thanks for your reply. I tried one more time with the buttons and found if you press two at the same time you can adjust 'moire patterns'. adjusting the horizontal moire (whatever that is) caused the lines to dissapear at a specific +/- setting which I found with some playing around.

Can you tell me what the moire patterns are all about and how changing these settings may or may not affect other settings??

Thanks!

The easiest way to demonstrate moiré patterns is to take two pieces of window screen material, place them together one on top of the other, and hold them up to the light, looking through the layers. If you rotate one layer with respect to the other, you will see a pattern that changes with the relative position of the layers.

In the case of a high-res monitor, this comes about because of the interaction between the CRT dot-pattern and the raster scan lines. Adjusting these out involves a combination of very fine trace rotation and raster position. This has little or no effect otherwise.

Another place where moiré patterns come into play is when scanning a printed picture. There is often an interaction between the dots in the picture and the dots in the scanner's resolution. Slight changes in the angle of the scanned item on the scan-bed can make a big difference in the scanned image result.

As a side note, moiré patterns are one of the few things known that can move faster than the speed of light.