here is my take on the situation,
monitor works with mame no problems
game board works on other cabs no problem
that only leaves wiring from game board to monitor or power supply voltage low
first trace you wiring for the monitor video input signal and using continuity test/bleep test on your multimeter prove that the wiring has no breaks(also you manipulate the wire whilst the machine is on to see if this causes a problem)
then if everything checks out with this perfect then you need to set your multimeter to dc volts and a range of 20 volts and meter the game board edge connector,i can not remember if its jamma but if it is then you put the ground of the multimeter to pin 1 or 2 and the volts lead of the meter to pins 3 or 4---this will give you the +5v reading which should not be less than +5.05 and not more than +5.20
google for multimeter demonstrations if unsure how to do