Re: Apple II+ Flakey Inverse Characters

[wrodiger <wrodiger@gmail.com>]

On Jan 4, 3:29 pm, wrodiger <wrodi...@gmail.com> wrote:
> On Jan 4, 1:07 pm, dog_...@macgui.com (D Finnigan) wrote:
>
> > wrodiger wrote:
>
> > > Thanks in advance for any help,
>
> > Here is a repair guide which may help:http://macgui.com/kb/article/759
>
> Thanks, I'll take another look through this. I reseated and swapped a
> few of the IC's mentioned here to no avail the other day.
>
> Will

Update: I reseated all chips involved in the text display generation
to no avail. Further analysis showed bad characters in both INVERSE
and FLASH mode. I then went through the text display section of Jim
Sather's book "Understanding The Apple II" which describes the logic
at gate level (great book by the way!). Based on my analysis, I have
determined that this is likely a bad Character ROM because the bad
bits within the characters on the display are at stationary points
within the characters. By my reasoning, and looking at the bit
shifting circuitry, this points to the ROM as the source. I ordered a
replacement from arcadecomponents.com (a good source of replacement
parts). I'll post an update when I receive this replacement and test.

Will