I think I've figured out a way to isolate between monitor and card on
my own computer.
When I press the adjustment button on the monitor the display the
comes up (brightness, vertical size, etc.) is produced by the monitor
itself -- not the computer. Also, on bootup the DOSlike screen that
appears (motherboard and bios data, memory check, etc.) does not use
the video adapter.
So, when the jitter starts I pop up the monitor adjustment display and
if it jitters it's the monitor. Then I reboot and pause the startup
process while it's showing the bios data. Again if it jitters it's
the monitor. But in this latter method it must jitter almost all the
time, and mine is intermittent. It may jitter for a minute or so and
then go away for a couple of hours. So the first method is preferable
because you can see the part of the screen driven by the card and at
the same time see the one supplied by the monitor.
If this analysis is correct the monitor is the problem.
