Alright, just got back from resistor shopping, but I have had a second though on this while creeping along in my car. So before I go though this HV exercise I do something else.
We know, G1 looks very suspicious as I have measured there the instability while elsewhere there is little to none instability that stands out in any way. And here we are on to something I believe. For fun and gigles, I put 220nF 250V capacitors to ground on both sides of R50. This seems to tame these flareups right down and gives almost a constant brightness but without much control over it. With the Sharpness I could kind of live with altho I would want the image to be sharp.
Please bear with me here for a second as I explain my theory. I checked on ebay, and found two such CRT monitors offered, both seem to have noticeable screen burn-in's as bad as mine. Sure this could just mean operators cranked up the brightness with little regard to CRT life, but I suspect a design flaw here. I believe many of these CRT of this type suffer from the same issue. Someone suggested to look for contamination that could offer a creep path for high voltage I looked the CRT socket as suggested and as many have found problems there, at least on some TV. So at the CRT socket life is good, but what about on the other end of the connection ?
The thing that kept me up at last night is that this thing flares up in brightness not down, this means G1 gets more positive. Confirmed as seen in the video I took of G1. Everything is stable at some DC on G1 and then suddenly I see the G1 rise erratically just to settle back down to about the same DC for a while and then this spectacle repeats.
I suspect intermittent creep currents but not inside the CRT tube, but outside of it.
Looking at the PCB diagram, G1 (GRN) is located right next to G2 (RED) on this PCB, perhaps separated by about 4mm or even less than that. Other CRT connection are clustered in very close proximity there as well, except Yellow, the video signal on the Cathode. This signal is far away on the opposite side of the board and well clear of anything nearby.
So G2 (RED) sitting neatly at a healthy 567V just 4 mm away from G1 (GRN)....
Hmmmm....
I am not sure what the Layout guy was thinking when squishing these signals this tightly together and on top of that running a jumper J1 (G1) half across the board when he could have conveniently have G1 (GRN) located at the other end of J1. Saving himself the trouble of putting the jumper, using up board space while easing up the CRT connection congestion.
Hmmmm....
Must have been a bad Monday, I guess....
My theory is that, I might have creep right there between GRN and RED, either on the component side or on the bottom. I suspect on the component side, its very crowded an the wires leading to the CRT socket have a little contact crimped to them which is then soldered into the board.
To confirm this theory I will dismantle this entire assembly to get good access to clean this board thoroughly, I will then apply something to add insulation to these connections, I am thinking using my wife's finger nail lacquer or perhaps some silicone. Then after reassembly I have a strong feeling the flareups will be gone.
The more I look at this exceptionally terrible layout design, the more I lean towards my theory.
What do you guys think ?
Does this sound reasonable for a theory ?