I've got a weird problem. I have a PVM 1342Q, an older model without an OSD service menu. The display occasionally works as expected, but most of the time the picture is extremely dark, with only bright blue or red areas showing up clearly on the screen. Bright white, gray, and black all show up as black. Mixed colors like brown, purple, or yellow don't show up either. I connected it to a PC by s-video and adjusted the color saturation, brightness, and contrast sliders on the PC and found that adjusting saturation made the blue and red areas much brighter, but adjusting contrast and brightness made no visible change at all.
It's almost like it's only displaying a chroma signal and missing the luma part, except I get the exact same problem with a composite signal as well.
When it works, it's usually right after turning on, then after a few minutes the picture snaps back to this no-luma mode. I don't have any RGB tables to test those inputs, only composite and s-video.