Thank you for your replies, Asimov and Jerry,

Asimov wrote:
It may be arcing internally. If you turn up the brightness to max and
it lessens or stops the symptom then that is it. If no change then it
may be a number of other causes.
This is definitely something I have to check. Brightness is pretty much the
only adjustment I haven't tried so far. Right now the monitor isn't
exhibiting the symptoms, but I shall check this out when the problem
inevitably returns.

Perhaps the arcing can be confirmed as it typically gives off acrid
smelling ozone gas and can be seen as corona or sparking effects in
the dark. Arcing can often be provoked by high humidity. Arcing also
tends to radiate interference to radio and TV.
I must say that I haven't smelled anything out of the ordinary. Nothing in
the very familiar ozone smell range anyway. I haven't noticed any problems
with RF reception either, nor do I remember hearing any crackling from the
monitor. I'll have to recheck all that though just to be sure.

You discussed vibration as not affecting the problem but many devices
may have heat sensitive internal joints which are not very sensitive
to vibration by comparision to cold solder joints. Among these are
electrolytic caps, resistors, transistors, IC's, etc.
True. My intention is to at some point open the case and use cold spray to
find any such heat sensitive components. There are, however, a lot of
components in a monitor, making it rather difficult to just start spraying
around, which is why I would have been interested in learning of any
starting spots anyone could suggest.

What is your repair experience? Remember there are lethal voltages
inside monitors.
I have fixed amplifiers and such in the past and done some focus tuning to
older monitors, and for those have spent considerable time learning about
the hazards of CRT monitors. I know where the dangerous parts are and would
rather read 10 books to find out about a component rather than poking it
with my finger to see what happens. This echoing the reasons for writing
here before even opening the case up so that I would have some idea of what
to look for.


Jerry G, thank you for your compliment. I like to write clear descriptions
because it not only helps others understand the problem precisely, it also
helps me outline the problem for myself.
I bought the monitor a couple of months ago used for about 100 EUR.
According to the backplate it's built in '99. Its history is such that the
person I bought it from had gotten it from his workplace where it had shown
the symptoms. He took it home and never had any problems with it. After I
brought it home, the problems were there, but were so rare that I figured it
was still worth the price I paid for it (this monitor has _excellent_ image
quality!) so we agreed that I'd be keeping it regardless of the problems. I
might still be able to take it back, but I'm not sure if I want to.
Nevertheless, considering this person never had any problems, it would seem
that humidity or some other environmental aspect could indeed play a major
role here.
I could take it to be repaired, but as you said, it would probably cost way
too much. Being the student that I am, I don't really have all that much
spare cash lying around to spend on this project or on a new monitor.

You guys have helped me already, particularly by mentioning the possibility
of arcing. I have a good multimeter and I can get my hands on an
oscilloscope if I need to. If it is about arcing though, I'd imagine that in
the best case scenario the whole problem can be fixed by a piece of
insulating tape somewhere.

Please do let me know if you have any further suggestions.
--

Arto Rantala