NES problem: vertical gray gradient on higher end BVM/PVM's?

[Dochartaigh]

My NES, on certain darker scenes, gives me a vertical gray/white gradient for the entire height of the screen. This is the end of the very first level of Super Mario Bros 3:



I know it's not the NES itself (tried my NESRGB via RGB and S-Video, and tried another non-modded NES with composite), and it's not this particular cartridge either (discovered this same issue on another game as well - another good test area is Ninja Gaiden - just let the cartridge play it's intro loop). **EDIT** tested this some more and the non-modded NES over component still does have this same issue, but it's so very faint you kinda have to turn your head sideways and squint to even see it - MUCH more prevalent on the NESRGB...

I used to think it was my BVM-D20F1U since it never showed up on my BVM-14F5U, and multiple PVM-20-14M2/14L2/1953/1354/etc., even JVC's and Panasonics etc. (all were roughly adjusted to display similar width pictures)...but I just got a PVM-20L5 and a BVM-20F1U and noticed all THREE of these monitors do this...so there goes the theory that it was this one single monitor. My consumer TV's with a RGB SCART>Component converter don't have this issue either.

The weirdest thing is on the D20F1U and 20F1U, when I adjust the H SIZE to be smaller (less wide) it goes away (see album link below) - but of course the screen is squashed at that point. I haven't tried changing this setting on the 20L5 (I do have a 20M4 I could test too). I was just wondering what this issue could be as multiple lower PVM-type models of all different brands, consumer TV's, etc., are all fine. It's just these higher end models. Not even a big problem as I've only seen it on a couple games, and only on a couple different gameplay areas, but it does drive me a little nuts, and overall I'm just really curious as to the "why"?

http://imgur.com/a/d4odX

[FBX]

I think it's because there's a white line off to the extreme edge of the NES signal in those circumstances, and the electron beam is sort of folding back in and 'leaking' that line onto the screen. This would explain why it goes away when you shrink the H-width. I don't know what the fix is though. Perhaps a recap might help, but I really don't know much about how these things work.

[Dochartaigh]

You might be onto something - seems like color bleed because it's rendering something light-colored offscreen...but I thought that whatever is off screen the electron beam wouldn't be trying to render/draw it you know? thus no interference or gradient ...just super weird.

Also don't think it's anything to do with caps (I could be totally wrong) since it's happening on three different monitors (two of them are from 2006 even) - and only the highest end ones do this. Probably something to do with the more stringent standards (for the 2x BVM's at least) broadcast monitors had in terms of their allowed signals maybe?

[FBX]

From what I understand, it has to do with how the electron beam isn't being fully shut off when it reaches the edge of the visible screen, and so it picks up that line on the edge and sort of smears it as the beam goes back to the other side of the screen to start the next scanline. I did some reading online and apparently the voltage is actually increased in order to stop the beam from happening as it creates less of a difference of voltage inside the tube. So I have to imagine it's something to do with the electronics that control when the voltage is upped in comparison to the edge of the screen. You'd want to be able to change that timing such that it happens sooner rather than later, so that the beam shuts off before it hits that extreme edge. Again though, pure speculation on my part, and I wouldn't know how to make that adjustment.

[Dochartaigh]

Just wanted to update this topic. I found 3x other people with this same exact problem, seems like they likewise are using NESRGB on higher end BVM's:

https://www.reddit.com/r/crtgaming/comm ... of_issues/

I'm going to post in the NESRGB topic as well and see if anybody there has experienced this as I would love to get to the bottom of this issue.

[Dochartaigh]

"H BLK" left and right, in the E Board Maintenance Menu on my BVM-D20 fixes this problem! I'm going to try it on my L5 and M4 as well and see if it'll fix it there.