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.

[rogerxyz]

Hi Zebidee, thank you for the reply!

I don't think this is an overscan issue - the last scanline is nowhere near the bottom of the screen. I've adjusted the vertical height way down so we can be sure there's no cropping on the top and bottom, and I'm going through the video modes in arcade OSD here:

https://drive.google.com/file/d/19tWdLeG8p_jrBBt_NsxS0sWWoReADpQX/view?usp=sharing

We can see that in some modes, for instance, 320x224@60 (15.66khz), the full image is drawn, you can see the bottom white border. Whereas the very close 320x248@59.97 (16.13khz) doesn't reach the bottom white border, and in fact, you can see that it in fact stops mid-scanline here...

My first thought is that anything over 15.6kHz can't be displayed by this Sony KV-XXX, but then 336x224@60 (15.66kHz) works fine but one at a little lower frequency 384x240@59.98 (15.65kHz) does not work.

Is there something here I can adjust in the range when generating modes, or the service menu, that could assist with these couple modes that appear not to be drawing the whole image? Or is maybe something else going on here - failure to sync is one thing, it obviously can display these modes, but cutting off scanlines is
something else...

My preset is

monitor "roger", "Sony KV-20FS100", "4:3"
        crt_range0 15625-16750, 56.0-65.00, 2.000, 4.700, 8.000, 0.064, 0.192, 1.024, 0, 0, 170, 262, 448, 526


I did just replace my modelines with the ntsc preset, rebooted, and it doesn't seem to have done anything.

Is this what foldover looks like? I thought foldover looked like the image "bouncing" off the top or the bottom and drawing again over top of itself, like it had been folded at the edge, but I could have a misconception.

[psakhis]

That game is 384x256@55hz.
Probably your tv isn't changing to PAL mode.

[Zebidee]

OK, saw the video. Overscan is not your real issue here.

Try NTSC presets (you tried that).

Try increasing the vertical size via service menu. Guess you tried that too.

Otherwise, I suspect TV is in early stages of vertical collapse. The main symptom is a shrunk picture, and may exhibit foldover (usually at top). Foldover will look like changing colours, much like you described. It can look like a really pronounced image reflection when quite bad. Should change (get worse) over time.

Changing the electrolytic caps, at least the ones near vertical deflection IC, may help.

Pull out the chassis and have a close look at all the caps. Failing caps might be bulging at top, might be leaking fluid. Sometimes failing caps show nothing, though an ESR meter can usually reveal them. You may need to solder, or find someone that can.

[rogerxyz]

Thank you again Zeb! It seems not unlikely that some issue in the deflection circuitry is to blame. Before I start putting together a cap list, I think one final test is in order:

I'll hook up another monitor - maybe a sibling Trinitron just for apples-to-apples - to the video card and see if it fares any better.

I just have to make some time for that....

[makya]

Hi, please post a log. Without we can only try to guess. However, that's a sure thing that ninja spirit will not display correctly using generic15 (according to my experience with euro TVs at least).

[Zebidee]

I looked at your video again, and your TV definitely doesn't like anything over 240p/480i. It cuts the bottom off anything over that, even 248p. It is clearly struggling to even sync with anything over 240p/480i (see the zigzag at top). Unsurprisingly, it seems to be an NTSC TV (says so right there), so use the NTSC monitor preset as your template.

If you've used the NTSC monitor preset to regenerate video modes properly, GM should not be selecting modes with vertical lines over 240p/480i.

An in-game log could help. That starting info screen can help too, as it provides video mode selection and screen sizing information. You can opt to hide them, but I prefer to leave them there.

Another matter is the suspected vertical collapse. Whether that line at top is foldover or not, I can't be 100% sure without a closer look, but the image definitely seems shrunken and now I notice it seems to have bit of pincushioning at the corners. It only gets worse over time, picture shrinking from top and bottom. Final stage is a single fat bright line across the middle. Replacing old caps may help and may help prevent other damage down the track.