On Sunday 27 April 2008 23:47, James Sweet wrote:

It appears you need to look at the schematic for a CRT monitor or TV to get
a better understanding of how this works. A disconnected cathode will float,
you have to pull it down towards ground to turn it on. The transistors
driving the cathodes isolate them from one another.


It depends on where the bad connection is, and the design of the cathode
driver circuits. It's also possible for one of the driver transistors to
have an intermittant short. I would desolder the blue cathode pin on the CRT
socket and tap the neck with the monitor on. If you can still repro the
symptoms, then the problem is probably in the tube.

I agree that I need to see schematics, or other sorts of documentation. As I
stated earlier, I'm reasonably well versed in audio electronics (built a HiFi
system from scratch), but CRTs are uncharted waters for me.

Anyway, about reproducing. I haven't been able to consistenty reproduce it.
Only about two maybe three times did the image seem to respond to me tapping
the neckboard or neck. Not enough to be sure.

And about disconnecting a gun; is that safe for the CRT? The repair FAQ warns
against running the CRT without the neckboard connected. Is having the other
guns connected enough protection against unintentional discharge, through the
glass or whatever?