Help troubleshooting Atari 800

[jerichoinbk]

Hi,

Last night I pulled out my family's Atari 800, so that we can play some M.U.L.E. and Dog Daze over the holidays (it's a kind of holiday tradition -- we've been very fortunate with how well the machine has held up over the last 34 years). Unfortunately, I ran into an issue last night.

 

Would anyone on this forum be able to help ID the problem based on my description below? I'm trying to figure out the extent or cause of the problem.

 

The machine boots up initially just fine, and will go to a DOS command screen (if the disk starts there), or to a "Game List" screen (not sure if that's what it's called), if it starts there. It will even begin loading a game ok ("beep beep beep", etc.). BUT -- as soon as it starts the game's graphics and/or sound for half a second, the screen freaks out -- lots of ghost images plastered around the screen, off-set graphic text, partially loaded images, etc., and it freezes. I tried hitting start, just to see if it can continue even w/weird graphics, and that's a no go. I also tried this with a dozen different disks & games, and it was all pretty much the same.

 

Given that the problem seems to begin when there is more memory intensive stuff going on, I am guessing (unfortunately) this is a memory chip or CPU issue. But I know very little about the insides of an Atari 800 -- as I say, we've been blessed with 30+ years of a (mostly) functioning machine.

 

Any guesses on the issue here? I can post more info if that helps, too, just let me know.

 

Thanks in advance for your help! I hate to be a newbie on a forum just asking for help w/o any help to offer others, and with much more limited knowledge. So thank you for your patience! Looking forward to learning.

 

-Josh

[Paul Westphal]

It's most likely ram. If you have more than 16k, take out all ram cards. The first card in the slots is the CPU card ( looking at it from the front ). Leave that one in. Test one ram card at a time, in the first slot, by running a basic cart. If it glitches, it's that ram card. I have some ram cards, best electronics, and B&C Computervisions does. If that's not the problem, its either the GTIA, OR THE CPU. If you take it apart, try to clean everything, including the ends of the cards, with a qtip and rubbing alcohol. If you need anything www.eightbitfix.com. Merry Cmas, and good luck.

[+Stephen]

Make sure there are no carts plugged in (BASIC). If you can, remove the "lid", and unplug and reseat the memory and OS modules.

[+bob1200xl]

Well...

 

If I told you to scope the REFRESH line and see if it is asserted for 280ns, could you do that?

 

No?

 

The issue is whether or not you can actually pinpoint the problem before you start replacing parts. In the majority of these cases, you can't, or it is so time-consuming that it is not worth the effort.

 

The most effective path is to just swap parts. Start with the memory cards and ROM, which are very easy to swap. Use parts from a known, good 800. If it still fails, swap out the CPU/display card, which requires you to dis-mantle your machine.

 

Best scenario is to get a working 800 and practice on that. Then, use it for parts.

 

Be aware - just re-seating these cards or ICs may resolve your problem. If you swap something and it starts working, put back the old part to see if it fails.

 

Good luck.

 

Bob

[Knimrod]

Had a similar issue when pulling my 800 out of mothballs.... I re-seated all the ICs that were socketed and it's been fine since. Kind if a pain to tear it down that far but it did work for me.. Good luck.

[jerichoinbk]

thanks, y'all! Will take a look into your many good suggestions when I have a chance, and let you know how it goes.

 

thanks for your help, and happy holidays!

[_The Doctor__]

almost any 800 that has failed for me was cured by pulling it out cleaning it and re-seating it...... only a few had the odd power supply or dirty sticky switch problem... followed by the dreaded task of either cleaning keyboard contacts or just pushing keys a million times to try to let them clean themselves....

 

lets face it the 800 is a tank.... I've seen them hurled across a room and re assembled... and keep on keeping on..... I bet you have a working 800 after a tear down cleaning and re-assembly... just pay attention and label what came from where... even the memory cards.... shouldn't matter but sometimes it does depending on what has been done to the 800, I had one that only recognized memory upgrades in a certain order and one that had a card that affected video clarity if plugged in one of the other slots... for whatever reason.....

Edited December 21, 2015 by _The Doctor__

[Mechanicjay]

You know, I have a couple memory intensive programs which will corrupt the screen as well, sometimes locking up the whole machine. I wonder if I shouldn't try swapping out my RAM cards....

[Kyle22]

It's most likely ram. If you have more than 16k, take out all ram cards. The first card in the slots is the CPU card ( looking at it from the front ). Leave that one in. Test one ram card at a time, in the first slot, by running a basic cart. If it glitches, it's that ram card. I have some ram cards, best electronics, and B&C Computervisions does. If that's not the problem, its either the GTIA, OR THE CPU. If you take it apart, try to clean everything, including the ends of the cards, with a qtip and rubbing alcohol. If you need anything www.eightbitfix.com. Merry Cmas, and good luck.

Good advise, but please note that the OS card is in front (when facing the keyboard), then 3 RAM cards or slots, and the CPU card is underneath the metal casting and not visible from the top. The CPU card also contains ANTIC & C/GTIA.

 

The 800 must be disassembled to access the CPU card.