More broken Apples...
falco at ihug.co.nz
falco at ihug.co.nz
Sun Apr 26 18:39:40 CDT 2009
> IIRC the Apple ][ text display was upper case only. The fact that your
> clone does lower case means there must be hardware differences between it
> and a real Apple. Which means, alas, the schematics for the latter aren't
> going to be a lot of use.
I think I might be luckier than that. As far as I can tell, the character
ROM in the Apple ][ is ASCIIish, but for some reason the lower case ASCII
positions contained upper case characters. This seems really strange to me;
why would Apple have done that? I can't think of any advantages. Maybe I'm
misunderstanding. Anyway, it appears that the clones tended to have true
lower-case characters in these positions. Looking at the board, it seems
identical to the II+ board I have - same ICs in the same positions, even
the printed text is the same and in the same locations. So, hopefully a II+
schematic will be of some use, though I wouldn't be surprised if there were
a few differences. I'll just have to believe the machine rather than the
schematic. I found several mistakes on the AppleColor monitor diagrams,
though perhaps those were for a very slightly different model.
> I would have expected ti to clear the screen to spaces at startup. That
> _may_ be 0010 0000 if the machine uses true ASCII codes in the video
> memeory. So maybe just bit 6 is playing up.
Aha, very good point. Paying attention to that would be worthwhile. General
question - would the entire RAM space be set to zeros at restart, or would
unused memory be left full of garbage?
> As others have suggested, reseat all the socketed ICs. If in doubt,
> replace the sockets!
Lots of work and time required... I could consider it though. It's probably
not justified for this clone, but if I can get the original II+ working,
that'll be a machine that means a lot to me, so I could consider it. I
recall hearing recommendations for the turned-pin style sockets.
> Then, assunming this thing uses 1 bit wide DRAMs
> (4116s, or similar), change the arounds. See ig you can make the stuck
> bit move somehwere else. If so, you know it's a RAM chip problem.
Good idea! I seem to recall that you can run one of these machines with
only 16k; perhaps first I should pull all the memory but the required 16k,
and go on from there. I'll have to find out whether I'm right, and if I am,
which set of 4116s (which is what it uses) is the correct 16k.
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