Hey Phil,
I have an UMK3 that i bought from someone.
works fine for 10min.(video and sound is 100%)
then slowly the game starts glitching where the colors all become yellow and there is wavy lines.
i have cleaned the jamma edge with alcohol
same result with 2 different midway cabinets with wells gardner monitors.
confirmed power is at 5.1 volts.
a bit unsure what to do next.