Apple Computer A original parts

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Macintosh_nik's picture
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Apple Computer A original parts

Hey, guys!

I recently received a replica circuit board of Apple Computer A. I must admit it is a great job, thanks Michael Ng!



My plan is to assemble this replica as close to the original photos as possible, although right now I'm going to have a pretty hard time acquiring the necessary components. I suspect that this build may not work as well as the later ByteShop and NTI production boards.


While I was waiting for the PCB to be delivered from Hong Kong I started studying the photo of the "wreck of history" sold at auction last year. Apple Computer A is quite seriously different from the production board, and it's not at all about the brown color of the board itself and the big orange capacitors. It's much more complicated than that, a lot of things are hard for me to explain, maybe together we can figure it out.


Resistors R20-R23 Allen Bradley 6.8 omhs, top row assuming the third stripe is gold. The silkscreen on the production board shows a value of 22ohms.Resistors R16-R19 Allen Bradley 1.2k (bottom row). The production board silkscreen shows a value of 1k.



More familiar to the modern enthusiast are the 3k resistors.



Orange Sprague 0.01uf and 0.001uf ceramic disk capacitors, not RMC or Circle D as on the production boards.



The blue film capacitors are 0.47uf, which is exactly midway between the 1uf as on the production silkscreen and the 0.1uf that ended up being used.



Blue 47pf capacitor instead of the usual Silver Mica to the right of the 27k capacitor.



Instead of the Fairchild IN914 diode to the right of the 330omhs resistor is a very old Hewlett Packard ITT series diode from the 60s, maybe even the 50s.



Not quite the usual 7.5k resistors with a fifth orange stripe. It does not seem to be Allen Bradley, unfortunately the true manufacturer has not been identified yet.