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. If I
turn it off back on, the display is still fine as long as I don't let the
ADM cool off first. Does anyone know what the problem might be? What to
look for?
Ohh, that's the exact signature of a bad elecrolytic cap in the vertical
drive circuit of the monitor. Many monitors of that vintage had bipolar
electrolytic caps in the vertical circuit. These may be hard to source, but
you should be able to find a suitable replacement.

Jon