26 Apr
2009
26 Apr
'09
4:39 p.m.
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.
Cheers,
Mike.