Re: A question about mono monitors

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

Tristan Mumford wrote:
> Hello!
>
> This is a semi A2 related post. It's about something I have noticed but
> cannot explain.
>
> Recently I tried what is apparently an exact clone Videx 80 column card in
> my //e. It sent my 1084S berzerk. I didn't think too much of it at the
> time.
>
> Today I built a fully accessorised XT. I chucked in a card I found with a
> composite out, figuring it was just a standard CGA card. It was a Persyst
> BoB, which is apparently some kind of super CGA card.
> Getting back to my point. I tried it with the 1084S. Same thing happened. So
> I dug a Micron 3 mono monitor out of the shed. It went berzerk too. After
> fiddling horizontal alignment until I got a stable image I concluded that
> it seems like the HSync is too fast.
>
> Would the Apple mono monitor have the same issue with the cards? It's the
> type with the internal vertical pivot for the CRT. I can't say the exact
> model because it's kind of buried in the shed right now.

80-column cards use a CRT controller chip, and its parameters are set
from the firmware in ROM.  If the parameters are wrong, the sweep
frequencies will be wrong.  Of course, it's unusual for a ROM's contents
to change.  ;-)

I used to have a Videx clone that produced some "flagging" of the raster
on the upper few lines, so I tweaked the parameters slightly and burned
another ROM to fix it.

(BTW, I think I know what caused my $E8 ROM to be shorted--I think that
someone before me put it into its socket reversed.  *That* would be
enough to short a ROM.  ;-)

-michael

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