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Atari 7800 video problems

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I recently got myself a 7800 and then had it modded with svideo. While most games on the system run fine, some run horribly. Specifically dig dug. The video is u stable and jittery, some games have weird artifacts or jailbars. Some games run un black and white and the screen is pushed down.... I bought a flash cart thinking that would help, and the results for these games are the same.

 

On camera dig dug looks fine put the video shakes up and down and the monsters glitch all over the place.

 

Do I need new caps, or voltage regulator? Can it even be fixed?

 

Thanks!

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Looks like you got the sideways mod :grin:

 

On a serious note, can you isolate the problem to 7800-specific games vs 2600 games?

Edited by ChildOfCv

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Looks like you got the sideways mod :grin:

 

On a serious note, can you isolate the problem to 7800-specific games vs 2600 games?

I think its limited to 2600 games, guessing my 2600 chip is bad, is this fixable without buying a new system?

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The video being jittery could also be your TV. I don't know the specifics on DigDug but many 2600 games don't use the proper scanline count for NTSC (even the NTSC games) and some modern TVs and scalers do not like it.

 

Can you test moon patrol and see if you get the title screen?

 

Aside from that the only thing that comes to mind is the TIA chip perhaps as it is still in charge of the video graphics in 2600 mode. I've s-video modded a few 7800s (Not this one) and I've never seen the Harmony menu look like that before. I'm going to send you a PM about this if that is okay?

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I've s-video modded a few 7800s (Not this one) and I've never seen the Harmony menu look like that before. I'm going to send you a PM about this if that is okay?

 

Yeah. At first I thought it be just the result of chroma/luma separation preventing the "blending" you usually see through RF and composite, maybe with an over-exposed photo. But then I saw a lot of graphical glitches at the end of each line.

If TIA doesn't turn out to be the issue, I'd have to suggest RIOT perhaps as an outside possibility.

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Yeah. At first I thought it be just the result of chroma/luma separation preventing the "blending" you usually see through RF and composite, maybe with an over-exposed photo. But then I saw a lot of graphical glitches at the end of each line.

If TIA doesn't turn out to be the issue, I'd have to suggest RIOT perhaps as an outside possibility.

This does happen to a degree but not enough for the menu to be completely illegible. Too bad he doesn't also have an UNOcart as that uses a similar method for displaying text I believe.

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The text issue looks like it's not properly interleaving the video lines, but instead writing the odd lines and the even lines in the same vertical space. That seems like a video sync issue. Of course if, as Crossbow says, it isn't writing full-spec NTSC lines, this might be the result of the TV's digital processors not sensing the even/odd interleave sequence.

 

On vertical retraces there's supposed to be a sequence of wide sync pulses that warned the ancient TVs to rearm the vertical sweep followed by skinny sync pulses to set off the sweep, and there's supposed to be a different number of them based on even or odd lines. If the TV tries to interpret the signal too literally and the TIA isn't following the standard this closely, it's possible that it's interpreting it as always even or always odd. That's what it looks like, at least.

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The text issue looks like it's not properly interleaving the video lines, but instead writing the odd lines and the even lines in the same vertical space. That seems like a video sync issue. Of course if, as Crossbow says, it isn't writing full-spec NTSC lines, this might be the result of the TV's digital processors not sensing the even/odd interleave sequence.

 

On vertical retraces there's supposed to be a sequence of wide sync pulses that warned the ancient TVs to rearm the vertical sweep followed by skinny sync pulses to set off the sweep, and there's supposed to be a different number of them based on even or odd lines. If the TV tries to interpret the signal too literally and the TIA isn't following the standard this closely, it's possible that it's interpreting it as always even or always odd. That's what it looks like, at least.

 

He has actual text corruption taking place. All of those should be centered and left justified. There shouldn't be any characters being generated off the extreme left like is being shown here. If the characters were all being ran on a single scan line interleave, they would would all still be left justified properly just overlapping more or less at that point.

 

Here is screen capture from a YT video I made on a clien'ts 7800 that I recently s-video modded. This is without the color cycling enabled on the menu so this was a static image before I captured the still from the video.

 

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Thanks guys for all the replies. The issues also occur on a crt tv. Im now pretty sure I have a bad TIA :( will replacing the chip require saracficing another atari 2600?

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Thanks guys for all the replies. The issues also occur on a crt tv. Im now pretty sure I have a bad TIA :( will replacing the chip require saracficing another atari 2600?

 

You can buy TIA chips from Best Electronics or from resellers on eBay who've taken apart old systems for parts.

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OP said he bought the 7800 and then had it modded. Did he try 2600 games prior to the mod installation and were they fine or exhibiting the same behavior as they were post-mod?

 

Can it be the TIA if "most" games work? I thought with a dying TIA there would be more across the board glitches and issues.

Edited by AtariLeaf

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OP PM'd me back. It was modded with a UAV and yes there is some jail bars in 2600 mode with the UAV I've found. Although wire placement helps to reduce it quite a bit. The TIA colorburst is just noisy it seems. But the text corruption is NOT normal and I do suspect that either the TIA or the RIOT is to blame. I would start with the TIA.

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OP PM'd me back. It was modded with a UAV and yes there is some jail bars in 2600 mode with the UAV I've found. Although wire placement helps to reduce it quite a bit. The TIA colorburst is just noisy it seems. But the text corruption is NOT normal and I do suspect that either the TIA or the RIOT is to blame. I would start with the TIA.

Ordered a new TIA, that seems to be the general consensus on the problem :) Appreciate everyone's help!

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Would be curious to know if this works for you...because I actually ran into something very similiar earlier this week while installing a UAV into another AA members 7800. I first noticed it on the color display from the 7800 diag utility. The Middle row of colors were darker and basically looked exactly the same as the bottom row of colors?! It did this on both Composite and S-vid output but not from the RF out. So I knew the UAV was to blame somehow. Further testing displayed what looked like corrupted text on many games with menus like Dungeon Stalker and also on the Harmony as you were getting?! I finally traced down the issue. It would seem that the larger SMD IC near the artifact adjustment pot wasn't quite soldered down fully.

 

I discovered this using the old method of pressing down on stuff while in operation to see if something changes. Sure enough it did when I put additional pressure down on that IC. Since I can't really read anything on that IC (Too small for me) I don't know exactly which one it is and I couldn't tell which pin wasn't soldered down well. So I hit them all with a little heat and additional solder to make sure.

 

Problem was solved...so if the TIA doesn't take care of this, you might check and see if one of the components on the UAV isn't quite making good contact.

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Got a new TIA installed and that fixed about 99% of the problems but we are still having issues with Dig dug 2600 working. The screen bounces still and graphics are going all over the place. Its hard to capture, other than that pic in the OP. The installer has replaced the TIA, the RIOT, and the Ram. Still getting the same problems. Fyi the game works fine on other atari consoles. Any ideas?

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I believe DIG DUG is one of the games that use on-board RAM. Could be an issue with an address line on the cartrdige port or possibly a power issue? Do you have any other Atari carts that use the same "SARA" cartridge board? Some of the more common are Stargate/Defender II, Millipede, Junior Pac-Man, Crystal Castles or Dark Chambers. If those exhibit the same problem, it might help to figure things out.

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I believe DIG DUG is one of the games that use on-board RAM. Could be an issue with an address line on the cartrdige port or possibly a power issue? Do you have any other Atari carts that use the same "SARA" cartridge board? Some of the more common are Stargate/Defender II, Millipede, Junior Pac-Man, Crystal Castles or Dark Chambers. If those exhibit the same problem, it might help to figure things out.

 

I know the dig dug is fine as it works fine in other systems. Haven't tried those other games, but most 2600 games work fine just cant understand what could be broken on the system to cause the video to be unstable. Its only unstable when I move dig dug around and then the video jerks up and down also the sprites glitch into walls. I know its not the TIA, RIOT, or Ram. Could the Maria chip the issue with a 2600 game? Caps and voltage regulator were replaced too.

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I know the dig dug is fine as it works fine in other systems. Haven't tried those other games ...

 

Yes, I understand DIG DUG works in other systems. The reason I suggested those other specific games is because they use the same exact PCB design, complete with extra RAM, that DIG DUG uses. If they *ALSO* have problems, that might narrow down what's going on with your 7800.

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Yes, I understand DIG DUG works in other systems. The reason I suggested those other specific games is because they use the same exact PCB design, complete with extra RAM, that DIG DUG uses. If they *ALSO* have problems, that might narrow down what's going on with your 7800.

 

Ah my mistake. I emailed the installer that suggestion. If those did potentially suffer from the same problem any idea whats causing it?

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So...I have something to add to this thread.

 

This weekend I had a Sears Video Arcade II I picked up in not working condition. It would power on with the lights coming up, but screen change...not vertical lines...just dead on the logic side.

 

Replaced out the filter cap, voltage regulator and finally the TIA to get it back up and at least show me games. But...every single one of the games were bouncing all up and down or slightly askew and eventually the video would cut out totally. Changed the TIA again and now had the image staying on the screen, but still glitchy graphics and bouncing like it wasn't in sync. Tried to adjust the RF Modulator...nothing worked. I finally changed out the RIOT and Bingo! Screen is now steady as a rock and the graphics corruption is gone as well. But again this is with an SVA2 but I would image it could be something similar with the OPs 7800 as well. Since it only effects 260 games.

 

So..change the RIOT next and see what you get.

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