Re: IIPlus 40col screen problem

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <dnapoli-0510951208080001@mod163.ee.net>,
Dick Napoli <dnapoli@ee.net> wrote:
>    My IIPlus was working fine one day and the next day when I turned it on
> I could barely read the 40 column screen.  It looks like the bottom 4 rows
> of dots for each character are being displayed twice (in the top 4 and
> bottom 4 position).  Almost impossible to read this way.  Any one ever
> have this problem and if so what did you do about it?  

Sounds like a fault in the video circuitry, possibly with bit two of
the row counter for each character cell, or one of the address bits
going into the character generator ROM.

>    The graphics screens display properly

Hi-res _and_ Lo-res?  If Lo-Res is working then that definitely
narrows the problem down.  Try pushing down on the character generator
ROM to make sure it is seated properly.

I'll have to review the II+ video circuitry to be able to narrow it
down further.  I'm reasonably familiar with the much simpler circuitry
in the IIe, but I've never looked at the II+ in detail.

> and when I use the videx-clone 80 col card, it displays correctly.

Not surprising - the Videx video output does not make any use of the
motherboard video circuitry.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand