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Re: Apple II+ Flakey Inverse Characters

mwillegal wrote:

I think that you are on the right track.

A flakey 2513 was my first guess, but you indicated that it only
happened
in inverse mode.  This problem should not be dependant upon mode,
though it
may be more obvious in certain modes. I had a batch of NOS 2513 chips
where
about 50% of them had this issue.

Regards,
Mike Willegal

PS
the 341-0036 character rom part listed on the site you mention is not
a 2513 and is not compatible
with early Apple II motherboards.


Sounds like it's time for a 2716-to-2513 adapter.


On Jan 7, 9:13 am, wrodiger <wrodi...@gmail.com> wrote:


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






--
-michael

NadaNet and AppleCrate II: parallel computing for Apple II computers!
Home page: http://home.comcast.net/~mjmahon

"The wastebasket is our most important design
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