Atari 800XL Green Screen No Command Line

[Gpizano]

I have an Atari 800XL that is in really nice shape but it suffers from the green screen of death. I know it is putting out some kind of video signal because I route all my signals via the monitor port through a scart converter to my LCD TV, and when you turn on the Atari, it senses the video signal. But nothing comes up on the screen other then changing the color to green. (And, yes, if I play with the pot, it will change to red, blue, etc).

One of the great things about this machine is it all socketed. So, I have a working 600XL, and I have swapped EVERY chip from the 800XL (one at a time) into the 600XL, and all work perfectly. All chips on the 800XL are getting the 5V and all sockets and chips have been inspected for damage and cleaned with Deoxit. Power supplies have also been tested and I even have three power supplies with all working on the 600.

Like I say, EVERY chip has been swapped from the 800 into the 600 with no issues.

I have poured over the board with my magnifying glass looking for broken traces and there doesn't seem to be any work done to the motherboard.

Could the crystal cause this? Unfortunately, I don't have a logic tester or an oscilloscope to test logic on the motherboard... 

Any suggestions? (besides buying an oscilloscope!).

 

Gpizano 

[+Nezgar]

I would normally suspect OS ROM, MMU, and RAM - and the only IC's that's not directly interchangable between those two machines would be the RAM. Maybe start with a replacement set of 8x64kbit RAM chips?

 

Are any of the RAM chips in the 800XL hotter than others?

[+DrVenkman]

If you're getting video, even the green or red screens of a non-booting A8 computer, then your crystal is fine (the video signals are derived directly from the crystal by way of the GTIA chip). This symptom is a basic failure to boot. It could be caused by a bad OS ROM, bad MMU, or bad memory most commonly. Unfortunately, you can't swap DRAM chips between the two but as @Nezgar suggests, do any of the 8 DRAM chips get hotter than the others? If so, it's is probably shorted internally and needs to be replaced. 

 

[Gpizano]

Thanks for the looks and replies, guys.

 

I forgot to mention;

None of the chips are getting hot, other then the CPU after about 10 minutes, but it isn't "burn your finger" hot.. I would say slightly hotter then warm.

As well, all 8 ram chips were replaced with known good 4164-15's. Still no bootage. Note: none of the original RAM chips were getting hot before swappage or after.

The MMU works when swapped to the 600xl, as does the OS ROM.

 

[AeroDD]

I had an issue with my 800xl where sometimes I’d get a green screen and other times a black screen. It took swapping the PIA to get mine operational. 

[+Nezgar]

Hmm all 8 drams replaced eh? Hmm... maybe a bad socket or some other component as you suspected. The original sockets are only single wipe and might not provide good contact if broken, corroded, etc..

 

Might be interesting to see what happens with a tool such as Shoestring's RAM tester which is a replacement for the OS ROM - if it is able to present anything up on the screen at all, and if it might provide further hints.

 

It would be for a 27c128 type EPROM. If you don't have the means to program one PM me I can drop a programmed one in the mail.

[Gpizano]

11 hours ago, Nezgar said:

Hmm all 8 drams replaced eh? Hmm... maybe a bad socket or some other component as you suspected. The original sockets are only single wipe and might not provide good contact if broken, corroded, etc..

 

Might be interesting to see what happens with a tool such as Shoestring's RAM tester which is a replacement for the OS ROM - if it is able to present anything up on the screen at all, and if it might provide further hints.

 

It would be for a 27c128 type EPROM. If you don't have the means to program one PM me I can drop a programmed one in the mail.

Hmmm... I shall look into the RAM tester... would be a good tool for my toolbox. I'm sure I have a 27C128 (or similar) around here somewhere.

I think I may go back to basics as well. Time to get out the multimeter and start testing out the traces to make sure there is continuity between all the DRAM chips and other traces on the board. 

[Gpizano]

12 hours ago, AeroDD said:

I had an issue with my 800xl where sometimes I’d get a green screen and other times a black screen. It took swapping the PIA to get mine operational. 

Well, now that I have swapped each chip from the 800 into the 600, maybe it is time to start swapping the other way around individually. Maybe I'll tone out the sockets as well to make sure each pin is actually connecting.

[hueyjones70]

I currently have an 800XL with a similar problem. On Wednesday the computer was working correctly, on Friday when I turned it on it booted to self test so I took everything apart swapped out BASIC, then ROM, still self test. SYS CHECK indicated that all memory was OK then with the next boot attempt I got a dark green screen. Sometimes it boots to self test most times it boots to a dark green screen. Occasionally if I insert a BASIC cart it will boot to basic but the green screen is predominant.

 

[Beeblebrox]

PIA? Also despite a good report for ram which chips do you have in there currently (Mt?)  if so I'd replace them just in case. 

[hueyjones70]

Yesterday I removed the stock single wipe BASIC socket and cleaned off all of the old solder and flux and flattened out the solder rings. I checked each with a magnifying glass to insure there were no broken traces. I then installed a new double wipe socket. I used a generous amount of solder. After inserting the BASIC chip, everything worked to perfection.