On Friday, June 19, 2020 at 12:02:29 AM UTC-7, Tom Lake wrote:
I have an ADM-3A dumb terminal and when I first turn it on the display is squashed and the top line is mangled. After five minutes or so the display looks OK but is a little jumpy. After a few more minutes, the display is rock-solid and stays that way until the next time I turn it on cold.

Either some of the video adjustments are temperature-sensitive (not impossible,
but unlikely) or you have a mechanical stress issue; maybe cracked solder joints, maybe
a dirty connector.

If you know how to safe the CRT, you can open it up and exercise the connectors,
look at solder joints (especially at heavty wires or connector pins) and maybe tap
with a chopstick at various points DISTANT FROM the anode wire while power is on.

If you care about its function, do be gentle with the CRT; those are irreplaceable.