Getting Asteroids to look right on a TV

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This is one of my current projects. I have a full sized Asteroids in the garage, missing 2 capacitors for the vector monitor and i don't have the original mainboard yet. So, i'm putting a PC in it and a 19" TV...then will source the original rom's on Ebay for the legalities. 19" computer monitor would be the way forward and turn up the translucency in MAME or whatever...but i'm thinking that the 2 TV's i have in the basement would suit my purposes better. When is TV out not TV out ? when it's being used through DOS ! I've got a couple of TV out cards to work with an Apple 11" green screen monitor and they work very well indeed (so 15.75Mhz is fine), but am getting a poor display on the TV's, with noise etc on the screen. the image is about 75% clear, stable in the Horiz and Vertical but poor otherwise. Any tips to share, apart from buying an ArcadeVGA card?