Wiebe Cazemier wrote:
On Monday 28 April 2008 03:23, Wiebe Cazemier wrote:

OK, thanks. I will have a look soon if I can desolder the blue gun and see if
the screen still flashes blue. But first, I will look up all the parts after
the (blue) cathode driver transistor and use a strong magnifier glass to look
for broken solder joins and such.

I have the monitor running now without the blue gun connected. The fault
persists. When I turned it on, the screen flashed blue on and off like a
stroboscope. I was able to reproduce it by tapping the neckboard. Now that
it's warm, the fault is gone again.

There is one difference. Before, the screen would contract and expand and
eventually turn off when it did this, probably because the CRT driver (an
LM2413 BTW) was shorted to ground through the blue cathode.

Anyway, the fault seems to be in the tube, in the blue gun. I will try the
shaking method a bit more, and hopefully I don't have to take any drastic
measures. BTW, I read somewhere in one of the sci.repair faqs that you have to
tap the neck quite hard: "not enough to break it, but close". I don't really
dare to do that...
As a last(distasteful)resort you could discharge a cap
(~1000mfd 10-50volt)between pins with an intermittent
short in the blue gun.