Re: broken double hires

[shack@onyx.southwind.net (Randy Shackelford)]

Louis Schulman (louiss@gate.net) wrote:
: In <52c8mk$r4$1@mhadf.production.compuserve.com>, 100041.1464 <100041.1464@CompuServe.COM> writes:
: >Which parts of my Platinum //e are responsible for the double 
: >hires graphics?
: >It's not working anymore. Yesterday (maybe last month) double 
: >hires was running fine, now the screen is missing the half of the 
: >pixels.
: >The orig. (small) Apple 80 col/64KB card is ok, I tested it with 
: >another _simple_ //e.
: >Are there chips in the Platinum to change and so repair the double 
: >hires. I think everything else is working fine.

: There seems to be something missing from your question.  I assume you are
: using some video card?  At least on my //e, the standard 80 col card and video
: port don't give you double hi-res, you need a video card.

You only need 128K, a rev B or later logic board, and the jumper installed or
the little bowtie connected, depending on how old your extended 80 column 
card is, to get DHR. No "video card" needed.

: Given that, have you tested the video card?  What kind of monitor are you using?
: Have you tested that?

: To directly answer your question, double hi-res is firmware that resides in the 
: video rom.  That does not seem to be a likely cause of this kind of problem.

Nope, actually DHR is an artifact, a side effect of putting 128K in the //e.
The first revision of the //e didn't have it. There is no firmware support
for it; that's why you see packages like Beagle Graphics which add & commands
to Applesoft so you can write DHR programs. You only have assembly without 'em.

: What do you see?  When you say the pixels are missing, are they blank?  Do they
: work in other modes?

The best thing to check is whether the 80 column display works. It and DHR
are closely related.
--
Randy Shackelford
shack@southwind.net