Bad solder joint on the crt or power supply.
JAG
>The display exhibits multiple problems;
> A nasty moire type pattern
> Crackling, shorting type sounds
> Display collapses with each crack, which occur several per second.
>
>So far I have booted the unit a couple times to be sure it wasn't some
>temporary condition, and tonight I swapped out the analog board with no
>change.
>
>Any ideas? I am thinking maybe the tube is hosed, but I am unfamiliar with
>this type of failure. Fortunately I have no shortage of 57x donor machines,
>but I don't want to swap the tube if it isn't a likely fix.
It sure feels, smells more like a short than an open, but I will take
another look. Plus I did swap the entire analog board including the tin can
on the back of the CRT. What I may do next is pop off the back and power
the unit up in a dark room tonight.
BTW what do you mean exactly by bad solder joint on the CRT?
*** update
I took off the back and booted the system in a dark room just now, and the
light show is all from the inside of the neck of the CRT. With the power
off I don't "see" any damaged areas, but it sure was active with the power
on, flashes, glowing areas that looked almost like embers, very sci fi.
This must mean the CRT is toast right? or could something else cause
this?(given the whole analog board was swapped out with no change).