bit_slicer
New member
A few things I'm currently working on for a customer: 
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Nice work. Good to see a few more SMA boards being brought back to life.
The board in the second picture looks different to the others. Can you explain what the differences are (if any) in how the board operates? I ask as I have one just like it that needs a repair.
I'm hoping to be able to answer that question soon! I only had a chance to unpack them yesterday - will actually start working on them this week. I did make a couple of initial observations. First thing was how cheap-ass these things are, even by 1980's standards. Hand-drawn, double-sided, no solder mask. They look like hand-made breadboards. The manufacture looks very cut-rate with uneven solder leveling, some of the via platings are too tall for their through-holes. The components they used are garbage. Maybe it was just what was available that era, but they used the same crappy single-wipe DIP sockets that Atari used. Everything hand-soldered, badly.
Second was that the board uses the six original mask ROMs from Missile Command along with two new EPROMs, presumably code patches to get from MC to SMA. That's interesting that they didn't burn completely new ROMs. Maybe it was a cost thing.
I can't wait to dig into these further! My main goal is to document the 'encryption' scheme (in quotes because now I'm wondering if it really is encryption and not something else) and generate a schematic for the board. Stay tuned for updates!![]()