Need help with strange graphical glitch on CX-2600A

[obi1kenobi1]

After years of wanting an Atari 2600 I finally decided to go ahead and buy one recently. My budget was pretty low, but I was able to find an untested lot with three CX-2600A systems, six joysticks, two sets of paddles, and around 30 games. I figured worst case scenario I could probably piece together a complete working system, but as it turns out all three work, and all but two joysticks work (those two have problems with the cables, the circuit boards still work well).

 

After trying out all of the games, though, I discovered a weird graphical problem with the "best" system (the one with the cleanest circuit board and case). It seems to be having trouble rendering sprites, on some games like Asteroids and River Raid about half of the sprites will glitch out and stretch across the screen, but they flicker in and out, sometimes appearing normally. It only happens on a select few games (the vast majority of games I tried showed no apparent issues), and the games play normally apart from this graphics issue (for example, collision detection still works on the stretched sprites). Also, these games work fine in the other two systems, so I know it isn't a problem with the game cartridges themselves.

 

That's probably going to be pretty hard to picture, so here are a couple of gifs of the problem:

 

 

First is Asteroids, note the orange and purple rocks. Both always display the same glitches (orange stretched way out, purple only slightly glitchy) and the other two are always normal.

 

 

Second is River Raid, this one is much more noticeable. About half of the sprites remain normal while the others occasionally stretch across the screen. Also, as you can see collision detection is still working on the problem sprites, making this one almost unplayable.

 

I'm wondering if anyone knows what the problem is and how to fix it. I'm able to solder and desolder components, but I don't have access to electrical equipment to do any kind of diagnostics apart from just turning on the Atari and seeing if it works. I have the other two working units if I need to actually replace any parts, but if possible I'd like to fix rather than replace so that all three work well. Also, just to be clear, this is the CX-2600A model with every component together on one small circuit board.

Edited February 28, 2014 by obi1kenobi1

[dankcomputing]

Swap out the TIA for a known good one, see if the problem persists. Check internal voltages. Also try a different RIOT chip, though you usually can’t even get ingame when those go bad.

[TomelloSoulMan]

Indeed, looks like a TIA issue

[+-^CrossBow^-]

You guys realize the original post was from back in 2014 right? 

[dankcomputing]

I know but they went to all the trouble of making GIFs of the glitches and nobody responded. Gotta reward that level of effort on principle.

Edited May 13, 2022 by dankcomputing

[+-^CrossBow^-]

11 hours ago, dankcomputing said:

I know but they went to all the trouble of making GIFs of the glitches and nobody responded. Gotta reward that level of effort on principle.

The poster hasn't visited the site since March of 2014 either. Or at least they haven't under that user account. So I'm not sure they will ever see these replies? I'm all for providing assistance to get people systems up and going again but unless the original poster eventually comes back to state if the issue was resolved or not, it doesn't help much.

 

 

[Trinity]

It helps me, just in case I ever run into that kind of problem.

[Thomas Jentzsch]

On 5/13/2022 at 6:17 PM, -^CrossBow^- said:

The poster hasn't visited the site since March of 2014 either.

Last visited: 20h ago.

[+-^CrossBow^-]

22 minutes ago, Thomas Jentzsch said:

Last visited: 20h ago.

Well, that is recent because that wasn't the case when I posted that.

 

[obi1kenobi1]

OK fine, you’ve awoken me from my slumber. I’ll admit it was kind of funny to get those emails replying to a post on a forum that I forgot I even had an account for (I remembered making a post looking for help, but I forgot where I had posted it). But with all the recent discussions I figured I should finally log back in to confirm that I did see these replies.

 

As an update I never did figure out what was wrong with it, as far as I’m aware it still has this issue. But while the most “mint” Atari in the lot displayed this issue the uglier ones worked fine, so I kept one of those around to play games on until I could finally fix the good one. I still have the glitchy Atari sitting on a shelf with my other consoles (basically a display piece), but the working unit got put away years ago and off the top of my head I don’t really remember where it ended up. At some point I’ll try to dig it out and swap the TIA chips to see if that fixes the problem, but it’s not really at the top of my to-do list right now.

 

So to reassure everyone this was indeed helpful information, even if it is eight years later, but I don’t really know when I’ll get around to confirming whether that advice actually solves the problem. I’ll try to remember to post another reply when I do try the repair, but who knows when that will be…