Re: Weird Apple IIe display

[Michael J. Mahon <mjmahon@aol.com>]

Antoine Vignau <antoine.vignau@laposte.net> wrote:
> Thanks, Rich, you've been able to decypher the display code!
> I've reseated all chips with no success,
> av

In that case, it's time to look for a tiny crack in the trace going to the
relevant address pin, a cold solder joint on that pin of the socket, a
damaged socket, or a bad gate driving the relevant pin. 

If you have a logic probe, the pin will not be pulsing as the display
refreshes. You can then trace backward to the driving gate. If it's not
pulsing either, then the gate is bad. If it is pulsing, then somewhere
between the gate and the ROM address pin is an open circuit that you can
locate with an ohmmeter or continuity tester. 

But you may find that pushing or flexing in the area of the ROM fixes the
problem, at least intermittently. This is a good sign of a tiny crack in
the trace, a bad via (if the trace has one), or a cold solder joint.

Hope you find the problem!

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon