Possibly rarest Apple 1 ever for auction
applecorey at optonline.net
Sat Jul 23 10:30:38 CDT 2016
> On Jul 23, 2016, at 10:20 AM, Tothwolf <tothwolf at concentric.net> wrote:
>> On Sat, 23 Jul 2016, Corey Cohen wrote:
>> My guess is that is was a test board for Apple. There are some weird mods to the ram timing with a variable cap and to the negative supply that looks like they were experiments to figure out the tolerances of the chips. The board was wave soldered. You can't fake that on an Apple-1 because of what happens to the back of the board by the regulators. [...]
> If you mean the crinkle tin plate under the solder mask, that doesn't happen due to wave soldering. The heavy tin plate was applied that way in a separate process before the solder mask was applied to the board. It used to be common to do that to all sorts of boards in the 1970s-1980s. With modern boards, is much more common now to just leave exposed copper/gaps in the solder mask and allow those areas to take up solder from the wave soldering (or reflow) processes.
The crinkle is exaggerated by the heat from the wave soldering. Your right doesn't happen in modern boards because of how the tin was applied.
Mike Newton tried to reproduce the technique in China for his replicas. After many failed/peeling attempts he came close but even when wave soldered, it doesn't match the 1970's effect exactly, though it does crinkle.
The other thing with wave soldered boards is how the Vias get filled in. They sorta pucker, it's hard to explain but easy to show. You can fill the Vias by hand, but they don't look the same as a wave soldered board. In experiments I have tried a lot of different ways to replicate it. You can always tell the difference if you look under a loupe.
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