issue with an old Samsung monitor

[ckong]

I have an old 20" Samsung 15KHZ arcade monitor with a Kortek chassis (monitor is mounted horizontally), and I have a width problem with it. For instance when I play a MVS game I loose about 3/4 of an inch of game image on both left and right side of the monitor (the image is to width). I tried of course to adjust the 'horizontal sub position' pot and the 'h-hold' pot on the breakout pcb, but that didn't help. Neither did adjusting the 'H-position' pot on the chassis (it was already turned to the maximum clockwise).

in short, I don't see the complete image of my NeoGeo games. The odd thing is that I also tried it with a regular game PCB (gunbird 2, I know it is a vertical game, but I just connected it to my horizontal monitor for testing purposes), and then the image is too narrow; I have a remaing gap of about an inch, and I can't get the game image width enough to fill the screen. And then there also is a kind of steady swirl from top to bottom in the image (which doesn't show with my neogeo games).

What could be wrong?