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My friend has a Atari 800XL in mint condition. When the device was turned on, the only thing that appeared was a dark red screen. Another friend of mine figured that the memory chips were to blame, and he was nearly right: the memory chips were smoking hot. The memory chips were replaced with more advanced ones (Atari compatible of course) but the screen is still there.
What can I do to determine and fix the cause of the red screen (you could consider it the blue screen of death...)?
Super hot chips are usually dead chips. That said, with the Atari one common culprit is a bad power supply — certain models are known to go bad in a way that results in excessive voltage at the socket, which can easily fry multiple ICs on the motherboard.
So first step would be to verify the power supply is good (preferably by not connecting it to another machine!) Use a multimeter to check for steady 5V on the relevant pins. Note this diagram is viewing the socket, i.e. the back of the plug.
If the power supply is dead you can actually power these things from a USB wall wart if you put a cable together, I've even run one off the TV it was connected to!
Once that's been verified as good you you need to work out what else might be wrong. An oscilloscope/logic analyser is one way to do it, but far easier (especially if it's a socketed machine) is to swap ICs with a known good machine.
I had a machine that only showed dark red, and although this commonly seems to be the RAM or the GTIA, for me it just needed a replacement CPU which I managed to source easily enough online. Good luck!
Several chips come to mind that can cause this on an 800XL.
If you don't have a logic analyzer, scope or logic probe, your only real option is to swap IC chips with known good ones.
If you have any of the equipment above, the Atari field service manuals or SAM's Computerfacts available at Atari Mania will be of great service in your attempts to resurrect the XL.
I have a 600XL which came to me with a red screen of death, one of the first things I did was to remove and reseat the MMU IC (CO61618) after that the computer runs ok, but if your Atari does not you could have a dead MMU or one of the other ICs or memory failing. MMU is a really hard to find piece of hardware so first check other components.
