Strange vertical lines - hardware bug?

[w1k]

Hello again,

now i want fix problem with strange TV bug (?)

My first atari was in 1989 completely upgrade (320kb ram, 3x eprom, etc), but even then was a bad TV picture..

 

you can see it in this video

 

http://www.youtube.com/watch?v=pAbR6zO1wYk

 

photos:

 

what can be wrong?

[candle]

thats normal

those wider ones are ANTIC REFRESH activity periods, those narrower are for ANTIC accessing video data

[w1k]

thats normal

those wider ones are ANTIC REFRESH activity periods, those narrower are for ANTIC accessing video data

 

really? i have two computers (800xe).. one is good, one is bad.. hmm.. both have a gtia fabric fix

[candle]

compare sharpness on both units, if you like, do the super video modification - they will appear even sharper!

[+bob1200xl]

In general, what is wrong is that the high frequency signals do not have good paths to DC return (ground, if you prefer). This impresses voltages on all the signals relative to their 'distance' from the source. That's what you see on your screen. The higher the frequency, the more visible it is. The more current being drawn, the more visible it is. (that's why you 'see' Refresh so often - lots of current in the RAM)

 

What would be nice is a ground plane on the motherboard, which is what Atari did on the 1450. Huge difference on that guy.

 

We really need to start over on the Atari video... although you can get some pretty good results by making some changes.

 

Bob

 

 

 

Hello again,

now i want fix problem with strange TV bug (?)

My first atari was in 1989 completely upgrade (320kb ram, 3x eprom, etc), but even then was a bad TV picture..

 

you can see it in this video

 

http://www.youtube.com/watch?v=pAbR6zO1wYk

 

photos:

 

what can be wrong?

[w1k]

In general, what is wrong is that the high frequency signals do not have good paths to DC return (ground, if you prefer). This impresses voltages on all the signals relative to their 'distance' from the source. That's what you see on your screen. The higher the frequency, the more visible it is. The more current being drawn, the more visible it is. (that's why you 'see' Refresh so often - lots of current in the RAM)

 

What would be nice is a ground plane on the motherboard, which is what Atari did on the 1450. Huge difference on that guy.

 

We really need to start over on the Atari video... although you can get some pretty good results by making some changes.

 

Bob

 

 

 

Hello again,

now i want fix problem with strange TV bug (?)

My first atari was in 1989 completely upgrade (320kb ram, 3x eprom, etc), but even then was a bad TV picture..

 

you can see it in this video

what can be wrong?

 

if i understand, it's problem with signal.. but my english it's no good, then i don't understand everything..

 

can you tell me more about:

"that's why you 'see' Refresh so often - lots of current in the RAM) What would be nice is a ground plane on the motherboard, which is what Atari did on the 1450. Huge difference on that guy. We really need to start over on the Atari video... although you can get some pretty good results by making some changes."

[+bob1200xl]

The Atari motherboard is not designed properly if you want to improve the video. Lowering the output impedance of the drivers just increases the high frequency currents flowing into ground. This allows signals to leak into places where they do not belong. By improving the video bandwidth, you get to see things that should not be there. Ugly stuff.

 

Your screen shot seems to show color signals leaking into the LUMA circuits. Try setting the color to black and white - see if the lines go away.

 

Is this a 130XE? PAL?

 

You can also see this kind of thing if you use the composite signal on the s-video input.

 

Bob

 

 

In general, what is wrong is that the high frequency signals do not have good paths to DC return (ground, if you prefer). This impresses voltages on all the signals relative to their 'distance' from the source. That's what you see on your screen. The higher the frequency, the more visible it is. The more current being drawn, the more visible it is. (that's why you 'see' Refresh so often - lots of current in the RAM)

 

What would be nice is a ground plane on the motherboard, which is what Atari did on the 1450. Huge difference on that guy.

 

We really need to start over on the Atari video... although you can get some pretty good results by making some changes.

 

Bob

 

 

 

Hello again,

now i want fix problem with strange TV bug (?)

My first atari was in 1989 completely upgrade (320kb ram, 3x eprom, etc), but even then was a bad TV picture..

 

you can see it in this video

what can be wrong?

 

if i understand, it's problem with signal.. but my english it's no good, then i don't understand everything..

 

can you tell me more about:

"that's why you 'see' Refresh so often - lots of current in the RAM) What would be nice is a ground plane on the motherboard, which is what Atari did on the 1450. Huge difference on that guy. We really need to start over on the Atari video... although you can get some pretty good results by making some changes."

[Rybags]

Wasn't there a mod out there that suggested a switch on one of the outputs to cut down interference?

 

It was either colour or composite video - a case of sacrificing something you're not using to improve output of the other signals.

[w1k]

Wasn't there a mod out there that suggested a switch on one of the outputs to cut down interference?

 

It was either colour or composite video - a case of sacrificing something you're not using to improve output of the other signals.

 

maybe.. that atari have lot of hardware 'tuning', from 1989 - 3x eprom, 320kb ram, etc

[+bob1200xl]

Composite output essentially adds the CHROMA signal to the LUMA signal, which introduces video noise to s-video configurations. The very first video mod I made left the composite out - much better picture but you need composite for artifacting, if nothing else. So, people put in switches to connect or disconnect composite output.

 

Bob

 

 

 

Wasn't there a mod out there that suggested a switch on one of the outputs to cut down interference?

 

It was either colour or composite video - a case of sacrificing something you're not using to improve output of the other signals.

[Marius]

On 800XL I remember: when I remove one resistor (or capacitor) those vertical lines showed up too!

 

Putting that one back, did remove them again. I thought: when I could relocate that component, and find the same location on the XE motherboard, it might help to add that resistor (or capacitor; i can't remember) to decrease this problem.

 

I prefer my 800XL without those lines too, because I 'hate' these vertical lines.

 

It's a common problem, and not just one or two computers.

 

On some side-scrolling games (like river rescue) I really get 'sick' when I look to concentrated on the game. The game scrolls, but the background (with stripes) isn't. So that creates a real hypnotising screen (brrrrr).

 

Good luck on fixing!

Marius