gradual horizontal warping issue on CRT

[gique]

Hi all, First off, huge applause to calamity for all this amazing CRT-centric lovelyness!

 have spent the weekend setting up all my hardware and amazingly got everything up and running on my Taito Egret 3 with a Thomson monitor (it was v. cheap refurb)

So now everything is running, I have one final calibration problem, but am unsure wether its an Arcade OSD or groovymame issue.

My monitor is set to vertical for vertically scrolling shooters mainly. I'm using win7 and the super resolutions.

When playing a game in 15 Khz, there is some stretching going on, it's more scaled down at the top of my rotated screen than it is on the bottom creating a weird warping effect when anything is scrolling. (mocked up example image attached)

It seems that the bottom is scaled 100%, judging from calibration screens, and gradually scales to about 70% at the top.

As the screen is rotated to to vertical, I guess this means when in normal orientation it is an issue on the horizontal axis. I read that super resolutions have "shimmering" issues but I can't describe it like that, it's more like the warping you get on a "just" mode on a widescreen TV. but only squished on top (far side on a normal oriented monitor)

In interlaced mode on the desktop while in windows, the screen seems fine, judging from the Arcade OSD grid.

Can anyone suggest where to start on  solving this issue? The adjustment pots inside the cabinet dont seem to allow for this type of adjustment / compensation.

The photo attached is as much info on the monitor as I can get...

Thanks!!

[gique]

UPDATE : So I tried a PCB and checked the convergence test screen, luckily the test mode had a good fine grid so I could check thoroughly..

So the monitor seems to permanently have compression towards the right of the screen. its actually closer to 50% squashed at the absolute right side..

so I guess the next question is, can I make any adjustments on ArcadeOSD or Groovymame to compensate for it?

Thanks

[big10p]

Not that I can think of. Anyway, you'll be better off just getting the monitor fixed, I reckon.

[Calamity]

so I guess the next question is, can I make any adjustments on ArcadeOSD or Groovymame to compensate for it?

No.

That's an horizontal linearity problem. Investigate that chassis and check if there's some sort of coil to adjust horizontal linearity. I recommend you to be specially careful with this as it may be very delicate. Try searching about this topic in the monitor section.

[Paradroid]

That's an horizontal linearity problem.

Yes. Many CRTs have horizontal linearity issues due to the shape of the tube and design of the chassis. However, these issues (which are easy to spot on any game that has a continual horizontal scroll) are usually symmetrical in nature e.g. the image "squeezes" at the edges and "stretches" in the middle. Apparently flat screen CRTs had to employ extra circuitry to allow for half-decent H-Lin on a perfectly flat screen. Conversely, older analog chassis with more curved screens don't often show any linearity issues at all.

Most TVs and monitors have controls to correct vertical linearity (some Loewe digital chassis have a whole range of settings to allow near-perfect vertical linearity adjustment) but adjustments for horizontal linearity are uncommon.

If the issue is asymmetrical in nature (which seems to be the case from what you describe), the chassis could be faulty.