22 Sep
2014
22 Sep
'14
1:52 p.m.
On Sep 22, 2014, at 1:35 PM, David Williams <dave at willomail.co.uk> wrote:
Hmm, thought that might be the case. Guess I need to find a copy of
the schematics as it looks quite differrent to the board found in the ADM3a. I've also
noticed the brightness seem to flicker every second or so. May or may not be related.
Cheers,
Dave
It may be normal. It depends on how the various power supplies work. Old TVs would do
this, newer ones generally do not. It happens if the sweep quits while the electron beam
is still running and the accelerator voltage is still largely present. If the filtering
on the high voltage has substantial capacity and the thermal mass of the cathode is
significant, that will happen. In more modern designs things are likely to be more
optimized, with smaller filter capacitors and smaller cathodes, so the beam will quit much
more quickly.
For a particular model CRT display, the question would be whether other units of that same
model behave likewise. If not, then this would suggest something odd in the particular
unit.
paul
Another
terminal question. I have an ADM-5 here which works fine but
when switched off, the display colpases into a very bright vertical line
and then to a single point in the center of the screen. This then lasts
for about 10 seconds and always happens regardless of the brightness
setting. Question is, is this normal and if not, is it likely to damage
the phosphor over time?
This is not normal and is probably indicative of a problem
in the CRT
drive circuitry. A CRT based terminal is very much like a television in
this regard. (This behavior can show up on TVs and it is also not
normal there.)