naujoks Posted October 1, 2022 Share Posted October 1, 2022 I have an 800XL with black screen on powering up. Voltage tested fine (tried different PSUs), all but one IC are socketed and I swapped the ICs for known working one. Clock on CPU is fine. Cartridge doesn't play. Self test doesn't run. No sound coming from anything either. Getting nice bit of chatter on data and address line on CPU. Caps look clean and not bulged. Didn't see any dodgy solder joints. No ICs getting hot. Pretty stumped on this one. Any ideas what I could try? Quote Link to comment Share on other sites More sharing options...
Beeblebrox Posted October 1, 2022 Share Posted October 1, 2022 (edited) So can you confirm if: A) ram are MT brand B) you have replaced ram chips Black screen is usually either bad cpu or ram in the first instance. Edit: typo - did indeed mean MT brand heh heh Edited October 1, 2022 by Beeblebrox Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted October 1, 2022 Share Posted October 1, 2022 (edited) Did you mean MT brand? I just don't remember any Beeblebrox ram chips Edited October 1, 2022 by Mclaneinc Quote Link to comment Share on other sites More sharing options...
Beeblebrox Posted October 1, 2022 Share Posted October 1, 2022 46 minutes ago, Mclaneinc said: Did you mean MT brand? I just don't remember any Beeblebrox ram chips heh heh - damn mobile phone. Error corrected. Yeah, didn't you ever hear of the Beeblebrox effect? Complete memory loss heh heh! 1 Quote Link to comment Share on other sites More sharing options...
naujoks Posted October 1, 2022 Author Share Posted October 1, 2022 RAM is Mitsubishi. I tested every IC, they're fine. Just for giggle I swapped them with a different set. Same result: black screen. Quote Link to comment Share on other sites More sharing options...
+scorpio_ny Posted October 1, 2022 Share Posted October 1, 2022 I had on of my 800XL’s that use go bad out the blue. Tried swapping chips, recapping and checking for broken solder joints. Nothing worked. I remember watching a repair video that they gently pressed on top some the larger IC’s while the board was on to see what happens. I did that and when I got to the OS rom, the computer gave a me a ready screen. On closer inspection, there was a pin with a broken weld at angle that was hard to see. You could try that. Just be very careful. 1 Quote Link to comment Share on other sites More sharing options...
Ricky Spanish Posted October 1, 2022 Share Posted October 1, 2022 6 hours ago, Mclaneinc said: Did you mean MT brand? So is there significant differences ? On my 1200XL it says NEC. Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted October 1, 2022 Share Posted October 1, 2022 Only in reliability, Commodore used them in a lot of C64's, and they just kept going bad, if you open a C64 that is faulty and see MT chips then they usually get swapped out even if not faulty.. Not heard anything bad re NEC chips.. 1 1 Quote Link to comment Share on other sites More sharing options...
+scorpio_ny Posted October 1, 2022 Share Posted October 1, 2022 4 minutes ago, Mclaneinc said: Only in reliability, Commodore used them in a lot of C64's, and they just kept going bad, if you open a C64 that is faulty and see MT chips then they usually get swapped out even if not faulty.. Not heard anything bad re NEC chips.. That has been my experience. I have repaired two Commodore boards that had this brand of RAM as source of the fault. If I happen on to a computer that has this brand installed, I will put it on my to do list to remove. I have a 130XE from my childhood that had MT RAM. Computer worked fine, but to eliminate a potential source of issues, I removed them all and replaced them with sockets and different brand of RAM chips. Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted October 1, 2022 Share Posted October 1, 2022 Good choice, it's not if they will go bad, it's when.. If you watch Adrian's Digital Basement, the second he opens up a machine with MT in it, his face just drops Thankfully, neither of my breadbins has them, nor my Atari's.. 1 Quote Link to comment Share on other sites More sharing options...
naujoks Posted October 1, 2022 Author Share Posted October 1, 2022 Yes, but back to my issue at hand... Quote Link to comment Share on other sites More sharing options...
Mclaneinc Posted October 1, 2022 Share Posted October 1, 2022 (edited) It's an odd one, you have changed everything inc ram and still black screen, when you turn it on does the monitor show the signal syncing? I presume you are using composite out rather than the most unlikely RF? Also, any mods of any kind on there? Edited October 1, 2022 by Mclaneinc Quote Link to comment Share on other sites More sharing options...
+remowilliams Posted October 2, 2022 Share Posted October 2, 2022 My original 800XL stopped functioning a short while back. Got around to looking at it lately - voltages were fine, and ultimately every single IC tested fine either by swapping into another working unit, or by testing in my BackBit Chip Tester Pro. This is a fully socked 800XL, except.. for one IC. That IC is U29 (the Delay Line IC) - and guess what, it was bad. Replaced it and the entire system was perfectly functional again. 2 Quote Link to comment Share on other sites More sharing options...
naujoks Posted October 2, 2022 Author Share Posted October 2, 2022 The same is the case here, Delay Line is not socketed so I haven't swapped it yet. Let me grab my desoldering gun. 1 Quote Link to comment Share on other sites More sharing options...
naujoks Posted October 2, 2022 Author Share Posted October 2, 2022 Well I'll be... It WAS the Delay Line IC! All up and running now. Thanks for the help! 7 Quote Link to comment Share on other sites More sharing options...
Ricky Spanish Posted October 2, 2022 Share Posted October 2, 2022 found this; Quote Link to comment Share on other sites More sharing options...
bfollowell Posted October 2, 2022 Share Posted October 2, 2022 Congratulations on finding the problem and getting your 800XL going again! I have an 800XL with mystery problems as well, and have swapped pretty much everything except for the delay line chip. I'd thought of eventually replacing the whole memory circuit with one of Lotharek's SRAM modules. Since the delay circuit is one of the last things I haven't checked, I may go ahead and order an SRAM to help confirm or rule out memory problems. Quote Link to comment Share on other sites More sharing options...
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