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.)
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.
The brightness flickers on almost every ADM-5 I've come across due to
intermittent poor contact in the brightness control.
I once had a problem with one of mine where the display collapsed to a vertical
line and then slowly faded out, however, I had not switched it off. This was
due to a bad solder joint on a leg of one of the transformers on the monitor
board. I think it was the horizontal driver transformer rather than the output
transformer. The joint failed when I had the terminal open to work on a
different problem with it.
I tried it just now and when I switch it off, the display collapses quite
quickly in both horizontal and vertical axes and fades very rapidly. I did
not see a vertical line at any point and only see a bright dot in the centre
for a short time if I switch back on quickly before the CRT heater has cooled.
(The brightness also flickered until I fiddled with the brightness control...)
As Mike Loewen suggested earlier in the thread, I wonder has the CRT been
replaced by one with a longer than usual persistence?
The monitor circuit does not have horizontal or vertical oscillators and relies
on drive from the logic board to enable horizontal and vertical scanning of
the CRT to take place. I wonder could a problem in the power supply cause the
power to the logic board to decay more rapidly at switch off than the monitor
power supply?
I have another ADM-5 which has a logic fault which I have failed to fix using
hints from the ADM-3A schematics. I have not managed to find any schematics
for the ADM-5 and I would be interested in a copy if you manage to find them.
Regards,
Peter Coghlan.
