Newsgroups: comp.sys.mac.hardware
Path: cantaloupe.srv.cs.cmu.edu!das-news.harvard.edu!noc.near.net!howland.reston.ans.net!agate!apple!mumbo.apple.com!pcnntp.apple.com!gateway.qm.apple.com!Dale_Adams
From: Dale_Adams@gateway.qm.apple.com (Dale Adams)
Subject: Re: Quadra 950 marginal video?
Sender: news@pcnntp.apple.com
Message-ID: <1993Apr23.131106.9201@pcnntp.apple.com>
Date: Fri, 23 Apr 1993 13:11:06 GMT
References: <1993Apr23.055934.1967@galileo.cc.rochester.edu>
Organization: Apple Computer, Inc.,  Cupertino, CA
Lines: 32

In article <1993Apr23.055934.1967@galileo.cc.rochester.edu> 
carlo@merlin.cvs.rochester.edu (Carlo Tiana) writes:
> We are having a problem with a Quadra 950 that has stumped a couple of
> techs sent to us by the vendor, as well as us :-)
> This Quadra is 'stuffed' with 64Mb RAM, 2Mb VRAM and some large disk (400Mb
> I think). What happens is that after a certain variable interval of time
> the video circuitry 'loses' vertical sync. It is quite apparent that the
> Mac CPU is still ok, and the problem really seems to lie with the video
> circuitry, since you can still save your documents, quit your aplpications,
> even pull down menus etc. (only the display is scrolling lik crazy, so it's
> pretty hard to hit menu items ;-)

[... other info deleted ...]

> Has anyone any ideas? Please? Please email as well as posting cause I seem
> to be spending a lot of time rebooting my mac lately and have a lot less
> time available to read news! :-)

Are you sure it's not a problem caused by software?  I've seen this sort 
of effect when a runaway program (which could be caused by an INIT 
conflict, for instance) accidentally wacks on a register in the video 
hardware.  Have you tried booting with no extensions and then letting the 
Q950 just sit there in the Finder?  You might also want to try changing to 
24-bit addressing (yes, I know you can't access your full 64 MB of RAM - 
it's just an experiment) as the video hardware registers can't be accessed 
then.

Another thing to try as a 'recovery' measure is to use something like 
QuickKeys to change the pixel depth of the display.  This reprograms (some 
of) the video hardware registers and may allow sync to be restored.

- Dale Adams
