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yell0w_lantern

Atari 400 Disemboweled and Killed

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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 by yell0w_lantern

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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.

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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!

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