Re: Apple II 'Super II' motherboard from 1981

[nathan@visi.com (Nathan Mates)]

In article <54uqk5$jqb@nntp.ucs.ubc.ca>,
Tim Shoppa <shoppa@alph02.triumf.ca> wrote:
>Don't forget that Apple's production machines in 1981 also had socketed
>chips.

   Ah yes, until the Apple III convinced them this was a bad idea. :)
>>   There'a a set of 6 easy solder/cut points in the mid-right; X1 and X5
>>   are connected, the rest are open.

>Do these look like they're more closely connected to the clock logic
>or the RAM decode logic?

   Hmmm, did a little more tracing. X6 looks like some kind of shift
key mod support. On once side, it heads off to pin 13 of the 16-pin
game port (Ann 2), while the other goes to pin 24 (shift) of the
keyboard connector.

   The others are a lot more of a pain to trace down. (At least the
board itself is made of the translucent plastic; I can hold it up to a
desk light and figure out where the heck everything heads off to :)
The top of X4 and X5 go back to pin 9 of the 74LS02 (OR gates? Been
quite some time since I even tried hardware hackery) that's right of
the processor and near the transistor package. X4's bottom goes to
motherboard ground, while X5's bottom heads off to somewhere under the
74LS154, and then scoots off in another direction I can't follow.

   X3 appears to connect off to pin 4 of the game port, pushbutton 2.
If it was connected, it't be driven by the power bus on the top of the
motherboard (ground? +5V?). X2 appears to be some sort of alternate
power connecting between the top side of the motherboard's power bus
and the bottom. [And also has a thick lead going off to the 'NE558N
8128' in the white socket near the game port] 

   The clock circuitry appears to be in the lower left near the actual
oscillator; the ram decode logic is probably mostly in the MMU below and
right of the processor.

>  I'm just extrapolating from my knowledge
>of the II+ here:  As there are only 8 RAM sockets on the motherboard
>and 256kbit DRAM wasn't even being sampled in '81, I doubt this is
>for anything as fancy as allowing 256kbit memory.  

   The ram chips have 'Japan 1G1T HM4864-3' on them with a small Apple
logo right of the 3. By the '64' in them, I'd expect them to be 64K
total from the 8.

Nathan Mates

--
<*> Nathan Mates http://www.visi.com/~nathan/      <*>
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