My Dig-Dug Atari original upright has all of it's original parts intact, including the monitor. Everything is fine, except that darned monitor! I have no idea what's wrong with it, but if it it involves any modification to the monitor itself, I'll just buy a new one since it has some Degauss and Burn-in problems anyway.
Here's a video of it's problems; read the comments section for the symptoms I wrote down. The video quality isn't that good, but the symptoms combined with the viewable video should work enough.
[youtube]NbDVYQltyNs[/youtube]
Here's a diagram showing the various stages that it goes through:
Stage 1: First noticed around 1:08 in the video
-Screen is very bright.
-Screen is very wavy.
-Screen won't fill the entire right side
-Screen has bad wrap over
Stage 2: First noticed around 1:09 in the video (mostly obscured by my hand)
-Screen gets jittery lines and strangeness on the right side
-Roughly every 800 milliseconds the lines and oddness pulse
Stage 3: First seen around 1:12 in the video
-Screen shrinks a lot
-Screen is very dark
-The top is too dark to see anything
-Partial scanlines are visible
Stage 4: This is the start of the video
-As screen gets progressively brighter, the screen gets very wavy
-A very blocky sine wave appears on the top
-After about 20 seconds it jumps back to Stage 1