"You want a Screw Driver? No thanks, just had one..."

Now back to the technical stuff....

A 'dry joint' - incorrectly soldered joint of the cable to the pin in the monitor is a very likely cause - if the production line gets a glitch - all the cables in a particular run may have at least one faulty join. I had hassles with several monitors in the past - one of the pins being bent due to ham-fisted clods plugging the monitor in forcefully - on more than one occasion.