Unusual CRT monitor screen symptom no one has been able to recognize (yet)

[chaos7]

I have a kortek KTX-26 chassis and Zenith CRT from a LAI NEO-GEO cabinet (and it was used in a lot of LAI early 90’s cabinets). A have 2 NEO GEO 6 slot cabinets (both left unused in storage for 15 years) so to isolate the cause I swapped the MV6 board, game power supply, chassis, game carts and even ran the power cable to the chassis from the other cabinet but trying all these thing never made a different so I believe it must be the CRT or interference from something. My other identical NEO cabinet works fine and the filament in the CRT neck is just as bright. One technician said it likely be a high voltage problem without seeing it. There is no arching at all. I went through a huge monitor repair guide consisting of over 115000 words but unfortunately nothing was mentioned that fit my symptom (but I did learn plenty of other things from it).

The effect on the screen is flickering rectangle dots that consistently flash all over the screen. I haven’t noticed a pattern, it just seem to flicker/flash like rain drops. The dots are white and they become more or less noticeable depending on how bright the screen is with video graphic changes. It is most noticeable when the screen changes between bright and dark - like when the NEO GEO logo pops up on the screen. Changing the G2 control on chassis does not fix the issue and will only alter how noticeable it is when the screen is dark or not (which is useless with video game graphics constantly changing. I have read power source can give interference even if from down the street but unsure why my other cabinet is not effected.

It would be really great if someone could give me advice on how to fix this monitor issue or at least has heard or read of it happening to someone else (hopefully on this site), and the name of the symptom (if it has ever been given one) as it may give me a new direction to search for. I will attach a few links to some tiny mp4’s to notice the flashing tiny horizontal lines/dots (never mind the vertical lines in the logo pics as I have since fixed that gameboard glitch). I am very surprised that with so many users on the site with arcades I can’t find any post mentioning the same type of issue.

https://drive.google.com/file/d/11E7JFgL2vhl2mmk-dqZDwBKXXuMVUdhZ/view?usp=sharing

https://drive.google.com/file/d/1F15Dy-EeI5YdxeTGHwKI79urjyvgmcws/view?usp=sharing

https://drive.google.com/file/d/10OxvfDrQvX7yVynHZqDOEM8BZX5S-lZW/view?usp=sharing

[grantspain]

do you have a marquee light, if so disconnect the power to it

check the crt dag earth to the neck card

i have seen this issue on polo 1 chassis when there is a resistor burnt out in the brightness circuit but never seen this on a kortek

[chaos7]

I have continuity from the ground wire connected from the wire along the crt to the neck board plus as well as to the chassis. It doesn't have any fluro light as its a MV6 neo geo, but I tried with out turning it on and running the video cable from my other identical cabinet back to back but problem still remains with the crt in the same cabinet and swapping every thing over except the tube makes no difference. The chassis works fine when I put it in the other cabinet so that eliminates any problem with the chassis or neck board. It is a very peculiar problem.

[grantspain]

some kind of earth issue or noise through the mains power
if you have a standard jamma type supply you could try linking the earth and common

[chaos7]

When I put my 2 identical cabinets back to back and plug in the monitor power and video cables from the cabinet that works fine, the issue remains on the crt screen on the other cabinet. When I had tried it in reverse with the cabinet with the flicker dots being plugged with the power and video cables to the good identical cabinet it works just fine like the cabinet always does using it's own game and power source. Each time I swap the chassis between the cabinets I reconnect them the same way.
I am very frustrated I can't figure it out over weeks and wish is was just as simple as a ground/earth wire that need to be removed/added.

[grantspain]

same tube number?

[chaos7]

Solved my issue. Even though my identical cabinet (inside and out) had a earth/ground wire from the chassis mounting screw to the mains power box I just unscrewed the wire in the cabinet with the issue and the problem was resolved. A bit odd but I'm not looking as to how coz it works fine now.

[grantspain]

noise going through the earth, glad you fixed it