no, it's not the 50/60 pot and I wish people would stop suggesting that. that's vertical linearity, that has nothing to do with this
Konami wired the 3 pin sync plug with composite sync jumpered between vertical and horizontal sync for reasoning I don't know. with all Wells-Gardner monitors this should be a problem but even still I don't really see curl problems because of how it's wired.
just move the plug over one spot or rotate the plug 90 degrees so sync is only running to pin 10 and you may need to adjust H. Hold again after but that should fix it
just move the plug over one spot or rotate the plug 90 degrees so sync is only running to pin 10 and you may need to adjust H. Hold again after but that should fix it
I still don't know why Konami wired those monitor plugs the way they did. a lot of them don't exhibit this problem but I suggest moving the sync plug over a pin just as an approach to fixing it.