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Twiggy Drive revision in 1985

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ried:
I recently picked up a couple of unpopulated and unused Twiggy analog and digital boards (from John W.). Interestingly, the digital board has a 1985 revision in the PCB.

Apple part number 853-0102 copyright 1982.
PCB obverse marked 820-0051-C copyright 1982.
PCB reverse marked 820-0051-C copyright 1985.





Did Apple really make a revision to the digital board more than a year after it was discontinued?

ried:
Just for posterity, here's a scan of the analog board also. It seems to be the older (?) and simpler revision that has "TWIGGY ANALOG BOARD" printed on the PCB, part number 820825A.





My working Twiggy drives do not feature that revision. Mine are the same, more complex configuration as this one, pictured below - borrowed from RR Auction (Del Yocam's machine). Does anyone know the story of why the analog board went through such a dramatic change?

ried:
Here's another one of the older (?) and simpler analog boards, shown below. This example is fully populated, marked 820825B and additionally reads SK T010-01. Seems to be a close relative to the bare board that John sent.

sigma7:

--- Quote from: ried on March 31, 2025, 08:24:04 pm ---My working Twiggy drives do not feature that revision.

--- End quote ---

Strangely enough, my set has one of each. Both are marked as Rev F.


--- Quote ---... more complex configuration

Does anyone know the story of why the analog board went through such a dramatic change?

--- End quote ---

AFAICT, they are the same circuit, the board layout was re-done. Comparing their styles, I suspect the less spread-out version was at the prototype stage, and only when the design was finalized was the board laid out again with the Apple logo and more detailed ground fill. I do wonder if there is any difference in performance and if the new layout was intended to address a known problem that contributed to the poor performance of the Twiggy.

A wild guess is the "1985" designation on the digital board is an error on the reproduction as the copper on the top side says 1982, and it is easy to be confused by looking at a backwards 2 in the x-ray view. One of my boards is 1982 in copper (on both sides), the other 1983 in copper (on both sides), with matching years on the silkscreen. Both are Rev H.

I see one of the older analog boards pictured is "E"; we don't yet have an accurate schematic history of the Twiggy analog board, are there more pics of that particular board?

Along those lines, are all of your Twiggy analog boards marked as Rev "F"?

ried:

--- Quote from: sigma7 on April 02, 2025, 04:10:40 pm ---I see one of the older analog boards pictured is "E"; we don't yet have an accurate schematic history of the Twiggy analog board, are there more pics of that particular board?

Along those lines, are all of your Twiggy analog boards marked as Rev "F"?

--- End quote ---

Here are a few more pictures of the "E" board: https://imgur.com/a/8xiL1I9

My working drives do indeed feature Rev "F" analog boards.

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