800xl sync problem with Mac/PC video-in

[eeun]

I've picked up an 800xl after being away from the hobby for many years. It's now had the Super Video mod done to it, and slightly un-done, as I've tried to sort out the problem below. I'm hoping one of you has gone through a similar experience and has a solution.

 

The problem is getting the Atari s-video or composite to sync on my PC or Mac video in. The image is good on a TV, but I want to use it on one of the computers.

 

On the PC, using an Adaptec Gamebridge, the image is overlaid with a skewed image of the same (pic attached).

 

On the Mac, using a MiroVideo 30 card, the screen is very clear, but the whole image sinks vertically about 1/4 of a screen, then pops back up...and this repeats, like a slight vertical sync problem.

 

I've tried holding different caps and resistors here and there, but my knowledge is limited, so it's largely trial and error and my chances of finding a solution on my own are slim.

[Marius]

I've picked up an 800xl after being away from the hobby for many years. It's now had the Super Video mod done to it, and slightly un-done, as I've tried to sort out the problem below. I'm hoping one of you has gone through a similar experience and has a solution.

 

The problem is getting the Atari s-video or composite to sync on my PC or Mac video in. The image is good on a TV, but I want to use it on one of the computers.

 

On the PC, using an Adaptec Gamebridge, the image is overlaid with a skewed image of the same (pic attached).

 

On the Mac, using a MiroVideo 30 card, the screen is very clear, but the whole image sinks vertically about 1/4 of a screen, then pops back up...and this repeats, like a slight vertical sync problem.

 

I've tried holding different caps and resistors here and there, but my knowledge is limited, so it's largely trial and error and my chances of finding a solution on my own are slim.

 

This problem lies in the fact that the atari does not produce a real 50Hz or 60Hz video output. Only half the scanlines are send the first, and the other half of the scanlines the second cycle are produced. Your Video capture card expects a clean 50Hz or 60Hz (PAL/NTSC) signal.

 

I have had this problem too with a TFT television. A cheap one. (Don't know if more expensive ones don't have that problem). That TV showed green lines between the some scanlines and a strange picture.

 

I think this is the same problem.

 

Perhaps you could change a setting on the PC/MAC software to handle odd/even scanlines that way.

Marius

[Rybags]

The Atari generates the same type of field continuously, whereas normal PAL does 312/313 frames.

 

My first capture card (an old Buster 2 with Zoran chipset) didn't work properly either - every second line would tend to hold an image persistently.

 

I've found that more modern cards tend to work fine.

 

But, they do make compromises, if you have control over de-interlace you might be able to change things a bit.

 

With de-interlacing, the card will tend to display at 25 Hz, blending 2 frames together, with each second frame filling in the normally blank scanlines.

 

Are you using RF, composite or S-Video input? I'd rate your best chance of success would be using S-Video, as it is the "cleanest" type of signal of the three.

[eeun]

I've tried composite, and s-video.

 

Unfortunately, neither platform allows control over the interlacing with the input devices I have.

 

I've tested the Gamebridge with a DVD player's s-video, and it's very good quality. But with the 800xl, as well as my 1040ST modified for s-video output (thanks, ppera!), but no luck.

 

The ST does work well going into the Mac, so at least I've got a solution for my 16-bit fix.

 

The darn thing is, the 800xl does display s-video properly on a couple of my older Macs, a Beige G3 and an 840av...but I need my G4 under the desk for work.

 

Maybe I'll just have to make room for a 13" TV, or try out one of those standalone video->VGA boxes.

[itaych]

Maybe I'll just have to make room for a 13" TV, or try out one of those standalone video->VGA boxes.

Just another thing for you to keep in mind: When displaying video through a PCI/USB capture device, there is usually a small delay incurred by the capture, deinterlace and display process. This is usually not too terrible when watching video, but when playing fast-action games the delay (of perhaps 2-4 frames) can become an issue. Maybe the standalone box really is your best solution, because those (or at least the ones I'm familiar with) have no frame memory and display what they receive immediately to VGA.

Another note is that standalone VGA converters output video in the same refresh rate as what they receive. Some monitors may have problems if your Atari is PAL, because 50 Hz is not always supported (CRTs are better at this than LCD). With NTSC you shouldn't have a problem, as 60 Hz is a standard refresh rate for PCs.

 

-itay