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

[Linards Ticmanis <ticmanis@gmx.de>]

Hi,

it looks like quite a few Apple programs, especially those released
after the //e became available, produce ugly artifacts on a ][+ board.
What I mean is the "magenta line" at the left of the screen that appears
when you extend the last bit of undisplayed memory into the display
range by having bit 7 set in the leftmost byte of a line of hi-res data
while the "undisplayed" bit is also set; this seems to be fixed on the
//e hardware.

Now this Apple II+ board that I have, a Rev. 7, was modified already, a
while ago, to include the change marked as "Rev. 8 or Rev. 9" in
Sather's "Understanding the Apple II" Figure 8.7.

Thus I have two unused NOR gates still left (the LS02 introduced during
the former mod has four of which only two are used). I think they could
be used to ensure that the hi-res delay flip-flop (74LS74 at A11) is fed
zeros during horizontal blanking, so that no undisplayed bit can make it
through to the display via the delay. My idea is to feed the term (NOT
(NOT hires-data OR hbl)), i.e. (hires-data AND NOT hbl), to that
flip-flop instead of plain hires-data, abusing one NOR gate as an
inverter by tying the inputs together.

The problem is that the copper trace to pin 12 of A11, which I need to
cut at a suitable point without destroying the connection between B4 pin
15 and A9 pins 2 and 15, is on the component side of the PCB and is
hidden below the socket on my board. The only usable image of the
Apple's PCB layout I could find on the net is from the Rev. 0 replica
project by Mike Willegal, and of course the Rev. 0 doesn't have that
flip-flop yet.

So my question is, does anybody have an unpopulated Apple II Rev. 7
board or an image of one, or maybe a board that uses sockets that don't
hide everything below them, as those on my board do. And could either
send me an image (of that board area) or check for me where this trace
runs when it comes out from under the socket and whether it can be cut
easily without destroying the other connection. Otherwise I'd have to
remove or destroy the socket which I'd rather not do if it can be avoided.

By the way, do you know if there is any software that needs the "magenta
line" to be present?

Thank you!

-- 
Linards Ticmanis