I don't know about Tekken 2, but the +12V rail is not usually used for anything other than audio, and sometimes lights. It shouldn't cause your picture fuzziness.
There should be a focus control on the monitor. It's usually a knob on the flyback - look for a wire with a suction cup going to the tube. The other end of that wire is connected to the flyback, and there should be one or two knobs on it. One for brightness, one for focus.
Also - post the type of monitor you have. I had one that had very low brightness and was very fuzzy, and it was an EEPROM that needed to be replaced.