yell0w_lantern Posted July 6, 2014 Share Posted July 6, 2014 (edited) I got a 2nd 400 from my uncle. It booted to a black screen. I pried out chips - the whole way in most cases but only part way for some and not at all for a few rather daunting ones. It seems he hacked together a RAM upgrade with some toggle switches to make different blocks of RAM visible if he wanted to play a pirated cartridge or something - lots of wires and stacked chips. Anyway, no change with re-seating I disassembled the working 400 and swapped boards from the non-working unit to the working unit (which he had also hacked - 48k and composite out). The power board checked out. The CPU board had different chip placement so I had to test it outside of the aluminum housing - it went to Memo pad but the screen rolled. I switched back to the working CPU board just to check and my working unit seemed fine - no roll, nothing amiss at all. Finally, swapped the RAM board from the non-working unit to the working unit and got a brown screen. I thought, "Aha!" I put the RAM board from the working unit into the non-working unit, and played with the toggle switches (they are unmarked, of course), and got to a blue screen that said "READY" and showed a prompt. Playing with the switches a little more, I got a cartridge to work. Satisfied that I had somewhat of a lead, I put everything back together they way it was before I started. My non-working unit still showed up black. But now my working unit showed only the brown screen (on both composite and RF). Ugh! Any ideas what I did to this poor thing? Edited July 6, 2014 by yell0w_lantern Quote Link to comment Share on other sites More sharing options...
Bryan Posted July 6, 2014 Share Posted July 6, 2014 I can offer a few insights... There are 2 types of CPU board but they are interchangeable. One has a standard 6502 and one has Atari's custom 6502C (Sally) CPU. The CPU's cannot be swapped. The best way to troubleshoot is to get a machine working and one by one try both chips of the same part number (C0XXXXX) in it to make sure they all work. If you can eliminate a bad part, it'll save you a lot of time later. Like I said above though, the C014806 CPU cannot be swapped for the 6502. Quote Link to comment Share on other sites More sharing options...
yell0w_lantern Posted July 6, 2014 Author Share Posted July 6, 2014 I called my uncle and he suggested a solder joint may have broken due to all the handling. I touched up every joint on the CPU board and... IT'S ALIVE! 3 Quote Link to comment Share on other sites More sharing options...
tep392 Posted July 8, 2014 Share Posted July 8, 2014 Congratulations! It's always nice to see another vintage computer saved. Quote Link to comment Share on other sites More sharing options...
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