Thanks Chris, so funny because my dad used to have a TV repair shop in the 60's, too bad I wasn't older and more interested! I'm really interested now and think my next purchase will be a Craftymech TPG.

Could be, that's getting pretty technical, the rings usually have paint on them so you can see if they have moved. Is it possible the yoke shifted??
Here is an excerpt from a TPG manual, it's basically answering why block patterns are used to indicate circuit health, it would be interesting to connect a TPG to your monitor, I have worked on boards that exhibit what's referred to as a tombstone effect (not quite square). Since I am borrowing their text, I will also include a link to their device at the very bottom:

The CHECKER pattern displays alternating black and white/red/green/blue boxes as in a
checker board.
This pattern is useful in checking the high voltage regulation of CRT power supply circuits.
Poor regulation results in trapezoidal looking pattern. For CRT type monitors with
insufficient power supply regulation can result in the corners of each box do not touch each
other as they should. This effect can sometimes be reduced by lowering the brightness or
contrast settings.
This pattern is also useful for checking ringing of the video signal as the signal transitions
from black to white. The abrupt, maximum change in CRT video drive current produced by
this pattern should not cause the voltage supplied to the video drive circuit to change in
display device with good voltage regulation. For display device with power supply that does
not have good regulation, softening or ringing in the pattern transitions can result.

https://www.arcade-museum.com/manuals-test-equipment/MT830A_User_Manual.pdf
https://www.ebay.com/itm/323882801012?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=Q5eZpeTKQcq&sssrc=2047675&ssuid=emm0sFORS4-&widget_ver=artemis&media=COPY
Just know, this device covers CGA up to VGA but it doesn't appear there is an option to invert colors. As such, RGB will not appear as RGB on Ceronix 1490, 1492, RGB1401 and other monitors that use an inverted color signal.
For inverted monitors I personally use a Craftymech TPG which covers Standard and Medium resolution only.

Chris

I have the same Tovis monitor. The gray wire you have is not hooked up at all on mine. The plug is open, no gray cable at all.

UPDATE: I bought the double diamond I mentioned but the motherboard and MPU were corrupt. So, I used these boards in the DD to get that machine spinning with the right payout and graphics. Now I am in search of both a motherboard and MPU that can run Triple Diamond Deluxe with HOPEFULLY the correct nudge. I will keep you updated once I obtain these two things. I also want to again thank everyone for the help you are giving me.

Look on the backplane.
The word "PRINTER" is etched on the circuit board right next to the 10-pin (J14) header socket...the 2nd one up from the bottom on the right.
All this stuff is available in the NLG File System, and you would have access to it, if you were a Contributing Member.

Double-click on drawing below to enlarge if needed...>>>

My backplane board does not have words on it either. 3902 13" GameKing cabinet. There is an 8-pin port labeled J12. Is this Netplex? I could not find my particular machine in the NLG File System (I am a contributing member.)