In article ,
Tom Lake wrote:
I have an ADM-3A dumb terminal and when I first turn it on the display is s=
quashed and the top line is mangled. After five minutes or so the display l=
ooks OK but is a little jumpy. After a few more minutes, the display is roc=
k-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 c=
ool off first. Does anyone know what the problem might be? What to look for=
?

A can of freeze-it spray, a plastic/otherwise completely insulated poking
device, and a very old soldered joint/failed component in the vertical
deflection section. Including inductors that may not quite be making contact
between the enamelled copper wire and its pins, capacitors/resistors with
hairline cracks in.

Once it's warmed up and "just about" working, cautiously poke, tap, or zap
with cold-spray and see if it fails.

Any sight/sound of arcing/sparking when it goes from working to not? If so,
observe it in low light conditions and keep your eyes open. Better still,
aim a camera at the board to see where it sparked, in case you miss it.
--
--------------------------------------+------------------------------------
Mike Brown: mjb[-at-]signal11.org.uk | http://www.signal11.org.uk