possible fault with the ribbon cable between cpu board and master display, or the headers for the ribon cable need cleaning,or cracked/dry solder joints on ribon cable headers if you have another ribbon cable try swaping it or try moving the plugs on the ribbon cable up and down while it is on and see if it runs properly,
My bk 2000 has the same problem, when i move the plug on the ribbon cable (cpu side) it works properley, try both ends


on another subject i noticed the top of the vortex is broken, if you want to fix the top of the votex here is a link to show you how http://www.stevechannel.com/pinbot.htm
just thought i would share it with you