OT?: failure modes of a RAMDAC

From: Carlos Murillo <cem14_at_cornell.edu>
Date: Mon Jul 3 22:11:35 2000

This is OT in that the piece of hardware that I'm looking
at (matrox millenium pci card) is newer than 10 years.
On the other hand, any comments on this might be
useful for older equipment as well. Here's the
scoop: the video card in my home computer suddenly
started acting flaky. The image flickers and has
diminished brightness; at first
I thought that it was the monitor, until I noticed
that the area inside the dialog window that pops up when
operating the setup menus in the monitor does not flicker and
has normal brightness. Aha, cable or connector, I thought.
So I tested another monitor. Exact same symptoms on the
second monitor. Ok, then a cold solder joint in the
card. I extracted the card and had a good look at it.
Nothing looks wrong. I put the thing back in and it still
had the flickering. Then, all of a sudden, brightness
jumps back to normal and everything works fine for the
rest of the session. Next day, I power up, and several
hours later the symptoms reappear suddenly. I am
thinking that the output of the RAMDAC is being severely
affected by something that diminishes its swing. As far
as I can tell, all colors are affected uniformly. The
flicker is random, does not appear to be tied to a given
frequency, and seems to affect the whole screen (refresh
is currently 85 Hz; changing it does not alleviate the
problem). So I wonder if there is some oscillation in
the output of the RAMDAC or an internal short that limits
the swing or what. Has anyone seen this sort of failure
before?

carlos.
Received on Mon Jul 03 2000 - 22:11:35 BST