Atari Asteroids / Wells 19V2000 HV Diode

There’s a wealth of information on old black & white vector monitors on the internet, so when the picture on my Asteroids ‘bloomed’ up much larger than it should be and became unstable I quickly found tips suggesting the high voltage diode was at fault.  However.. most of this information was actually written in Usenet times – text only documents!  I couldn’t actually find a picture anywhere of where this diode is.

So for anyone else searching, I’ve circled it in red in the photo.  I used a diode marked ‘VARO H598′ bought from Ebay which is not the original part, but comes recommended as a replacement, and indeed it works perfectly.

I should also point out you should make sure the monitor CRT is fully discharged before going near this part as the high voltage can be present even when the monitor is powered off.  Info on that can be found elsewhere on the internet.