I recently picked up a game with a Sanyo 14" color monitor which closely matches Atari Monitor TM151. The problem with the monitor is that a gradient test pattern of 16 levels only displays 8, with the rest of the gradient being the maximum color.
I know that's not the greatest description, so I've attached a picture of the Red test screen. Blue and Green are the same. If I adjust the bias pots, the lower half of the gradient fades/disappears, but the upper half stays constant - no gradient appears in the right hand part of the screen. The brightness at the front of the monitor and screen control on the neck only change the overall picture (as would be expected.)
If have tested the board (JROK Mylstar) on another monitor and confirmed that the gradient covers the entire screen, left to right, as shown on page 23 of the
MSF manual.
The monitor had been capped a couple of years ago (according to a sticker on the frame), but I don't know if the problem had presented before or after that point.
Any suggestions on where to look? The RGB path seems to keep the colors separate (3 of just about everything) so I can't determine what is shared between them that would have the same effect on all 3.
Thanks.