TrashPanda wrote on 2022-07-10, 03:48:
Might simply be old phosphor in the tube, the phosphor coating on CRTs doesnt last forever and will eventually degrade, it sound more like its the electron gun as it scans down the tube + old phosphor causing the black line. The brightness/darkness is likely bad pots that need replacing or adjusting, might also be worth checking voltages to see if components are getting stable/correct voltages.
Sadly as these old CRTs age (and yours sounds like its one of the older ones) they dont age well and eventually itll be one of the irreplicable parts that wears out such as the tube itself.
Used to be that your local electrician could fix CRTs but sadly most of that knowledge has either retired or is no longer with us.
Yeah, the monitor is an IBM 8515, which I believe would put it in the late 80's or the very early 90's, and it does have quite pronounced trailing as things move on a black background, so I'm assuming the tube itself isn't in its ideal state. It was actually originally from my local public school, so presumably it would have gotten a lot of use back in the day. Still, it's the only era-appropriate monitor I have that doesn't have egregious burn-in, so I have a rather vested interest in keeping it working as well as possible.
Oh, also, I want to clarify that it's not a black line, it's a very slightly dark line. Honestly, without a solid color background (like the default Win 3.1 desktop) it can be near impossible to see, it's just that with my OCD I hate knowing there's an imperfection like that.
I'm afraid I'm still rather a novice at working on stuff like this, so I wouldn't know where to even begin checking voltages and the like. There's a similar issue I have where, particularly visible in Sierra's old games, there are regular columns of dark areas across the screen, but I'm pretty sure that's somehow being caused by the way I have it wired up (since I remember it going away if I plugged the cable directly into the computer), combined with some oddity of the monitor itself because I haven't noticed it with an almost identical setup with another monitor.
Tiido wrote on 2022-07-10, 05:13:
Is the speed of motion constant or it sometimes goes faster/slower ?
I can only think of a power supply related problem, where there is some sort of a beat frequency with line deflection and PSU operating frequency and it manifests as this sort of effect on the video driver output. Monitors I see tend to have PSU synced with deflection so these sort of things won't/can't happen.
As far as I can tell it's always at the same rate.
darry wrote on 2022-07-10, 05:37:
Could that maybe be caused by a ground loop ?
I don't know, do VGA cables suffer from ground loops? If so I think that might explain the aforementioned dark columns, but I have absolutely no clue how I could go about fixing that. It's not like audio cables where there are ready-available isolators you can buy to fix the problem.
