Help Understanding CRT issue

[earthprime]

My trinitron CRT has an issue with its display, and I can't find a description of the issue (so I can learn how to fix it). On side-scrolling games (like SNES Castlevania) the sides of the picture appear to "roll" into place, as the image was being projected onto a sphere. It almost gives the image a 3D look, since the background doesn't remain in a straight line while scrolling across the screen. This has to be a common issue that I can fix with the service menu, but I first need assistance learning what its called!

[Xbytez]

It would be better if you posted a puicture of the issue.

A guess based on your description is it could be trapezoid or pincushion settings, not sure if your Trinitron has these settings available for adjustment.

[earthprime]

Attached are two videos of the issue.

In the 1st (PXL_20211107_224708306.mp4) - you can see the issue by focusing on the bricks in the wall, beneath the player stats and time. You may need to watch it a few times, but you can see the bricks "bow" downward as they reach the edge of the right-screen. It also seems to be happening in the middle of the screen beneath the player health bar.

In the second (PXL_20211107_233143641.mp4), you can see the colors in the background wall. They appear to curve downward as they move away from the center of the screen. Put the video on continual playback - you might have to watch for about 20 seconds, but you start to see the effect.

Also a test pattern picture, which shows the 'bow' effect:

PXL_20211107_234410439.jpg (5.09 MiB) Viewed 4407 times

[earthprime]

Looks like this issue is caused by bad "linearity". I have a Trinitron KV-27FS13. Any assistance for how to correct this is much appreciated (i.e. service menu settings?)

[callanabrown]

I think you have relatively good geometry from a flatscreen trinitron. They're just never very good in my opinion, if you are sensitive to horizontal linearity issues.

I have a little 9" TV/DVD flatscreen and it has terrible left-to-right stretching, terrible for scrolling games.

[FoxbatStargazer]

The proper fix involves opening up the TV and moving or adding small magnets to the tube to straighten things out. Which is pretty tricky/dangerous as you need the TV on while doing it, and it is a lot of tedious work, that even people who have gone through it are not sure it is worth it.

Not easy to find rando consumer american TVs as sharp as the flatscreen WEGAs but in general, bubble/rounded screens have far fewer issues in this area.

[akeley]

There's no such thing as a perfect CRT, especially in 2021. If you find one with ideal linearity, it'll most likely have something else off. You're better off accepting the flaws -which were always part of the deal anyway - and enjoying the benefits. Besides, most of these issues only really exist when you think about and look out for them. Once you let go and start playing games, they don't matter that much anymore.

And if it's really bad and you really can't get used to it, it's probably better to start looking for another set. As Foxbat says, these adjustments are not beginner-level and can be a rabbit hole even for experienced TV-tweakers.

[Xbytez]

As others posters have noted unless you know what you are doing around the high voltages inside a CRT (being potentially lethal with a possibility to kill you) I would leave it alone. However you may be able to correct somewhat using a service menu.

Personally my opinion from your picture, it shows uniform convergence issues on both the left and right of the image near the middle, I think it might be your deflection yoke slightly out of alignment.

[Jegriva]

Try to get into the service menu, most of the remote codes are documented. But, still, bear in mind that you are NEVER going to get the perfect picture. Especially if you, like I do, late-CRT-era "flat" screen.

[Jason]

Hello, everyone, i'm new here.

Sorry for bringing this back but the photo up there is very appropriate for my question: would it be possible to create a tool through MiSTer FPGA which if it can't fix a similar geometry issue, at least alleviate the problem?

[dmckean]

The place to be doing geometry adjustments is in the service menu. It's really not too difficult, just write down all the default settings before you start messing around. You need to really get a feel for all the adjustments and what they do and know that many settings interact with each other.

While flat tubes have tend to have a lot of issues, they also have more adjustments in the service menu to deal with them. And once you do get them adjusted, they look good from all angles and not just head on like bubble shaped tubes.