Re: Getting rid of the infamous "magenta line" on a Rev. 7 II+ board.

[Linards Ticmanis <ticmanis@gmx.de>]

Just in case you're interested, my original idea with HBL didn't work
out because it seems like that signal rises and falls much too early, so
I got stuff cut off at the right edge of the screen instead of at the
left. However, using the enable signal for the Video Muxer (Pin 13 on
A10 to Pin 7 on A9) instead worked like a charm. This is really nothing
else than the composite "video blanking" signal, but suitably delayed by
LD194. Now the ugly artifact is gone, without cutting off anything "of
value" at the left edge of the screen.

So the complete plan for Rev.1 up to whatever was the last pre-RFI
revision of the mainboard is as follows (the pin assignment should be
compatible with the Rev. 8/Rev. 9 color killer mod):

First of all, let me STRESS that I make no guarantees that this works on
your Apple and is error-free. If you blow your Apple (or your house),
don't blame me. I'd recommend using your brains and a set of schematics
to verify the correctness of the following instructions before you start.

If you don't happen to have a Rev. 8 or Rev. 9 board that already has
the necessary 74LS02 chip at A14, put a 14-pint DIP socket in the rework
area at A14. Connect GND to pin 7 and +5V to pin 14 of this socket.

Wire:
A10-13 to A14-8 and A14-9
A14-10 to A14-11
A9-2 to A14-12
A11-12 to A14-13

Cut the trace from A11-12 going towards A9-2. On Rev. 7 at least, it's
on the component side, and it can be cut between A11 and A10 (Thanks
Mike Willegal!). For a first test, it's probably better to follow Mike's
advice and solder directly to pin 12 of A11 while removing that pin from
the socket, instead of cutting the trace right away. Double-check all
connections, making sure you didn't create any accidental shorts between
adjacent pins.

Put a 74LS02 in the socket you added at A14, making sure orientation is
correct.

Make sure you don't short your mainboard with bits of spilled solder or
wire leftovers when you put it down for the first test!! I've made it a
habit to wipe off the working desk surface before every power-on after I
once killed a Mac board this way.

For a first test, this procedure is handy, since it works without a
language card or a keyboard plugged in and with less than 48K (so no
need to put that one RAM from the language card back into the mainboard
at E3): Before you start doing any modifications, format a DOS 3.3
floppy, MASTER CREATE it, then store this short BASIC test program as
HELLO, adapted from Sather:

10 HGR:HCOLOR=5:HPLOT 5,0 TO 5,159

Then you just have to plug in a Disk II card in any slot and boot, to
see whether your mod succeeded.

This should work with all Rev. 1 and newer Apple II and II+ boards,
except that from what I see in Sather, the RFI boards seem to lack the
rework area at A14 (and the 74LS02 that Apple themselves put there is
already "fully booked" for the sync and color killer changes of that
board, so it won't work to use it for this mod). This means that on a
RFI board you'll have to mount the chip differently.

-- 
Linards Ticmanis