Atari 800 Graphics Glitch

[Novarolla05]

Hello all, this is my first post to this forum, but I've been reading and learning a lot here for quite a while, so thank you all for that!

 

I'm pretty new to the A8 line, and finally got my first one, a plain 800, 48k, and 810 drive. Everything worked fine at first, then I noticed some games had a single column of triangles and random artifacts near the right side of the screen. Not every game did this. The ones I have that do are Pole Position, Frogger, and Blue Max (most obvious). Frogger is the hardest to notice, it shows up as "gaps" in the logs/turtles. I figured it might be some bad RAM, so I swapped out for known good RAM, and the problem on all games is still there. I've inspected pins, and re-seated every chip in the thing twice. My next guess would be either something on the OS board or the processor board, but I have zero experience and limited diagnostic tools.

 

Not sure if it's related, but the mountains in Rescue on Fractalus are all sorts of messed up. Could just be a bad .atr file though...

 

Just trying to get some expert opinions before I just start replacing every chip/board one at a time. I can take more pics if needed. Thanks in advance for advice anyone might have!

 

-Rich

[Faicuai]

Mhmm... surprised that 15 hours have passed and not a single answer.

 

If I were you, I would jump straight to CPU board, and check ANTIC, 6502 and GTIA, in that order.

 

My pick would be ANTIC chip. A spare CPU board could allow you to  diagnose quickly and safely, before you start dealing with chip pulling, which needs to be done carefully so the underlying sockets don't come off their pins (I have seen this a few times, maybe due to age, etc.)

[Mclaneinc]

Just to check, is the picture via composite or RF...Just to rule out stuff..

[+Stephen]

2nd vote for ANTIC.

[Novarolla05]

Thank you all for the responses! I had a feeling it might be something on the processor board, I just like to be methodical, and get other's opinions before I just start throwing parts at it ?

 

I went ahead and ordered a good board from B&C. I'll let you know what happens when it gets here.

 

@mclaneinc I am just using RF for video.

[Sugarland]

Congrats!  Don't throw the old board away of course. The other chips on it should work fine and you might need them one day.  It's good practice to label the non functioning board as partially not working but for parts and store it in the 800's box so they are together.   Congrats on your new 800!! I just made an Atari 8bit introduction/tutorial video that you might like. Will upload to YT it in a day or two or three.

[Rybags]

Antic for sure.

It seems to be happening where there's wide DMA and/or horizontal scrolling enabled.

That arrow is screen code $FF so it's like Antic might be fetching the character code when it should only be doing a refresh cycle.

 

Do the unwanted characters move at all?

Also note your monitor is showing more overscan than would normally be seen on a TV and you can expect to sometimes see weird stuff if you have big overscan but not like this.

 

Request - if you do find it to be Antic at fault and replace it, don't throw the old one out.  This sort of thing is worth further research, might be natural ageing of the chip or something.

[Novarolla05]

Thanks! No worries, I pretty much never throw anything away, it's a habit I got from my dad...

 

On Pole Position and Frogger, the characters don't move at all, but on Blue Max while scrolling, they all shift one column to the left for a split second then go back, looks like they are flickering. I can try to run some other scrolling games to see what happens while I wait for parts.

 

@Rybags I'd be glad to help out with something like that, but how would you recommend documenting/researching it? I'm pretty ignorant when it comes to the nuts and bolts of electronics, I'm a steel and hydraulics man by trade.

 

-Rich

[Rybags]

The only practical way to research it would be to run a bunch of software tests to replicate the effect in a controlled way in various graphical configs.

I guess a decap might reveal something but not worth the trouble/expense.

My guess is the chip has probably just suffered some malfunction or maybe internal Ram failure - there's sufficient internal buffering for the wide mode's 48 characters and the failure looks to be occurring at around the 43rd one.

[Sugarland]

In the mean time you might want to try spraying some deoxit on all of the CPU card chips+sockets. Even though you reseated the chips twice that might not be enough to clean off corrosion.

[Sugarland]

Hi Novarolla5 here is the tutorial video I just made and posted here:

 

 

Hope it's helpful. Consider it merely a first attempt at teaching how to use the A8 platform.  Teaching of how to use them starts at the 8m mark. Cheers!

 

[Sugarland]

Nah now I'm not happy with that video. First eight minutes blabbering about the platform saying mostly nothing new that hasn't already been said on YouTube. Will redo it.

[Novarolla05]

Great news, got the new processor board in today, and no more glitches! Even Rescue on Fractalus displays the mountains correctly now, so apparently that was the problem there too.

 

Now that it's working right, I'm looking forward to diving into the thing, and seeing what it can do! Thank you all for your help with this, and let me know when you get your video ready, I'd love to check it out and learn some stuff.

 

Also, should I try to do anything with the old ANTIC?

[Sugarland]

Congrats!!! That was an easy fix. Your old Antic could be the cause but it was not narrowed down that far. If you want to you can move the old Antic onto the new board to see if the problem reoccurs. It's always best to move chips from the old broken items to the known-working since the old board _could_ have a root cause that broke the old antic that might break the new antic, hypothetically speaking.

 

I've re enabled the video I made and it should play now.  It's private and won't come up in searches. The first 8m merely introduces the different models and is skippable. It's not perfect and I could do a lot better. Of course I don't know the most about the platform but that video is meant as an introduction.

 

 

Edited April 11, 2020 by Sugarland

[Rybags]

What to do with old Antic - depends where you live.  There's plenty of people around who'd be able to perform software based tests to deduce what the problem is.

It would be interesting to know because such faults are rare - often Antic either works perfectly or is dead and does nothing.

[Novarolla05]

Great video for getting started in the hobby, good info on both emulation and real hardware!

 

FYI, I swapped my ‘bad’ antic onto the new board, and the glitch came back. Looks like it’s probably something wrong with antic. I didn’t put the ‘good’ antic on the old board just in case the board itself is what caused it, like was mentioned.

 

I live in the Wichita Kansas area, and I’m open to shipping it to someone for testing if they’re interested.

 

 

[BitCortex]

Whoa I just noticed that my "new" 800 has a similar issue. Blue Max has a column of flickering garbage all the way over on the right.

 

Also noticed issues in Ballblazer and H.E.R.O. Other games like Drol and Boulder Dash are perfect.

 

Ordered a new CPU board from B&C. Can't wait to see if it fixes this.

[_The Doctor__]

Just remember that some modern televisions may display garbage on the right due to decoding method and aspect ratio. In fact some ingenious devices have been made to mask the issue off. Mytek here on AA made some such devices....

[Mclaneinc]

Super glad to hear its working...

[+DrVenkman]

5 hours ago, BitCortex said:

Whoa I just noticed that my "new" 800 has a similar issue. Blue Max has a column of flickering garbage all the way over on the right.

 

Also noticed issues in Ballblazer and H.E.R.O. Other games like Drol and Boulder Dash are perfect.

 

Ordered a new CPU board from B&C. Can't wait to see if it fixes this.

A photo would be helpful to be sure what you’re seeing isn’t normal. Be aware that if you’re watching on a modern widescreen display, they often show video “junk” along the edge of the screen, stuff that would normally be beyond the edges of a 4:3 CRT display area and thus invisible. Some games are notoriously worse about this than others (Pole Position, for instance). 

[BitCortex]

3 hours ago, DrVenkman said:

A photo would be helpful to be sure what you’re seeing isn’t normal. Be aware that if you’re watching on a modern widescreen display, they often show video “junk” along the edge of the screen, stuff that would normally be beyond the edges of a 4:3 CRT display area and thus invisible. Some games are notoriously worse about this than others (Pole Position, for instance). 

 

OMG you're absolutely right ? The junk I'm seeing is actually correct! In fact, the Altirra emulator shows exactly the same junk when I enable its extended overscan mode (see screenshots below). Fascinating!

 

I'm actually getting a RetroTINK device to improve the 800 image. Hopefully it'll hide the artifacts ?

 

Thanks for responding!