Maxlean Posted May 23, 2022 Share Posted May 23, 2022 Ok guys, I'm stumped. I've got my original 800XL from 1985, and dug it out of storage a few months ago to start having some modern Atari fun. Fired it up and was greeted by a black screen. This machine has a Newell Industries 256k upgrade, btw. I deoxed all the sockets and re-seated the chips, and she came back to life, but was unstable. Ran the memory test, and it would produce errors, sometimes video corruption, and sometimes lock up. I removed the Newell 256k, but left the ram chips since I don't have the original 64k chips, but I've been told that this is fine, no change. Bought new 256k ram chips, (like 32 of them), and swapped them. Thought there was some improvement, but it'll still randomly fail the ram test, and sometimes has the video corruption, and still sometimes locks. Sometimes, it'll run for 10 minutes on the ram test with no faults. So I dug out my new in box 1200XL, which tests perfectly fine, and decided to swap chips, one at a time. Swapped the ram, ANTIC, GTIA, POKEY, CPU, and PIA, all one at time. Nothing changed. I haven't swapped the smaller ICs yet. I'm kinda leaning toward the MMU, but unfortunately, the 1200XL uses a different one, so I can't swap that, and of course can't swap the OS roms. I've also measured the power supply while running a failing mem test, and voltage is stable at 5.09v. Any suggestions? Thanks, Scott Quote Link to comment Share on other sites More sharing options...
erichenneke Posted May 23, 2022 Share Posted May 23, 2022 47 minutes ago, Maxlean said: Ok guys, I'm stumped. I've got my original 800XL from 1985, and dug it out of storage a few months ago to start having some modern Atari fun. Fired it up and was greeted by a black screen. This machine has a Newell Industries 256k upgrade, btw. I deoxed all the sockets and re-seated the chips, and she came back to life, but was unstable. Ran the memory test, and it would produce errors, sometimes video corruption, and sometimes lock up. I removed the Newell 256k, but left the ram chips since I don't have the original 64k chips, but I've been told that this is fine, no change. Bought new 256k ram chips, (like 32 of them), and swapped them. Thought there was some improvement, but it'll still randomly fail the ram test, and sometimes has the video corruption, and still sometimes locks. Sometimes, it'll run for 10 minutes on the ram test with no faults. So I dug out my new in box 1200XL, which tests perfectly fine, and decided to swap chips, one at a time. Swapped the ram, ANTIC, GTIA, POKEY, CPU, and PIA, all one at time. Nothing changed. I haven't swapped the smaller ICs yet. I'm kinda leaning toward the MMU, but unfortunately, the 1200XL uses a different one, so I can't swap that, and of course can't swap the OS roms. I've also measured the power supply while running a failing mem test, and voltage is stable at 5.09v. Any suggestions? Thanks, Scott Quote Link to comment Share on other sites More sharing options...
erichenneke Posted May 23, 2022 Share Posted May 23, 2022 Have you checked all the solder joints on the RAM sockets? Perhaps it's a bad/unreliable joint or two causing the erratic behavior. Might be worth just reflowing those to be sure. 1 Quote Link to comment Share on other sites More sharing options...
xrbrevin Posted May 23, 2022 Share Posted May 23, 2022 if you have an eprom burner you can make an MMU out of a GAL16V8D: Atari MMU (C061618).zip Quote Link to comment Share on other sites More sharing options...
_The Doctor__ Posted May 24, 2022 Share Posted May 24, 2022 failing sockets, normal solder reflow dance, make sure no oddball flecks of conductive material are under in or around the sockets/pcb legs/pads and replace electrolytic caps that may be letting noise etc. Then move on to the support chips and finally mmu 1 Quote Link to comment Share on other sites More sharing options...
ClausB Posted May 24, 2022 Share Posted May 24, 2022 You can use 256K chips in the XL but make sure pin 1 of each chip is pulled high. There's a resistor for that but it usually gets removed during the upgrade. 1 Quote Link to comment Share on other sites More sharing options...
Maxlean Posted May 26, 2022 Author Share Posted May 26, 2022 On 5/24/2022 at 5:20 AM, ClausB said: You can use 256K chips in the XL but make sure pin 1 of each chip is pulled high. There's a resistor for that but it usually gets removed during the upgrade. Yeah, I reinstalled the removed resistor. 3k ohms, I believe. Hadn’t thought about cold solder joints on the sockets, etc. I’ll check all that next. With as many times as I’ve removed and installed most of the chips, and cleaning with deoxit, I’d think they’re sparkly clean at this point. Lol. Quote Link to comment Share on other sites More sharing options...
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