Seibu SPI mobo/ pcb on 31 khz monitor

[spikehead]

Both SPI based games (VP 1 Japanese) and Raiden II flicker or freeze when I try to run them on a Sanwa 31 khz monitor using this scaler:
http://www.ebay.co.uk/itm/Arcade-game-R ... 1326060786"

Other jamma beasd games run fine if the resolution is set to 640*480.

I read somewhere that the Seibu boards have a quirky refresh rate and might cause problems. Am I missing something concerning the scaler or do I need other devices to make Seibu games run on the above mentioned monitor?

Thanks for your help.

[Wurstkopp]

Protip: Get this cab:
http://www.ebay.de/itm/Sega-Virtua-Stri ... 41655976e8",
build the Sanwa monitor in your Naomi, have fun forever.