crt_emudriver stopping mid-scanline?

[rogerxyz]

Hey all! I think I've been living with this problem for years and it never really registered that maybe something was wrong...

So, the full image isn't drawn to my CRT. I'd say in 240p, the bottom 10 lines or so are missing, and this is really weird, but it also stops drawing halfway through the last scanline.

Additionally, I'm guessing this is related, there's maybe an extra one or two scanlines above the top of my screen that are mostly white but changing colors. No pic because I adjusted my CRT to push that off the top and promptly forgot it was happening. But now that I'm actually giving this some thought, it's probably wrapping around and trying to draw the bottom part of the image before the first real scanline.

Is there anything I can do to diagnose and correct this? I am using a consumer 15khz NTSC TV, with VGA → GreenAntz → Component in. My crt_range is basically generic15 with some minor tweaking, but I can try to see if resetting it back to generic15 does anything.

Bottom of my screen in "ninja spirit" - you can see all but the first 3.5 lines of the HUD is missing.


What it's supposed to look like


This is just an example - the bottom appears to be cut off at some point in all progressive 15khz modes (in other words 240p and the surrounding range 220-244p or whatever).

Any ideas? Thank you very much!

[Zebidee]

Hey all! I think I've been living with this problem for years and it never really registered that maybe something was wrong...

So, the full image isn't drawn to my CRT. I'd say in 240p, the bottom 10 lines or so are missing, and this is really weird, but it also stops drawing halfway through the last scanline.

Hi Roger, that's "overscan", deliberately oversizing the picture by 2%-10%, a feature of most TVs. When just "watching TV", people want to image to fill the screen. It would look weird otherwise. Losing a few lines/pixels around the edges doesn't matter, because all the main action happens in the middle of the screen.

Overscan isn't great for gaming though.

For vertical size/overscan, mostly it is best to try to adjust within the TV's service mode. Do you already have access to that?

Unfortunately you can't do much about vertical size by adjusting CRT_emulator monitor presets (porch settings). This approach can give good results for horizontal overscan though.

Some other ideas:

- run games in a higher resolution - for example, running 224-240p games in 256p or even 264p. You can force this by [romname].ini files, or force GM's hand by only creating 256p modes (no 240p) in the first place.
- While running Groovymame and in-game, press TAB to access a menu and various video size slider controls.

Additionally, I'm guessing this is related, there's maybe an extra one or two scanlines above the top of my screen that are mostly white but changing colors. No pic because I adjusted my CRT to push that off the top and promptly forgot it was happening. But now that I'm actually giving this some thought, it's probably wrapping around and trying to draw the bottom part of the image before the first real scanline.

This may be "foldover", an early sign of the TV's vertical deflection circuit starting to fail. Most likely aging electrolytic capacitors. Your TV is likely 20-30 years old by now. It sounds very minor at this stage, but you may want to consider getting the TV recapped.