Congratulations on the new machine! Looks like original, unmolested boards in that machine!
0 on the LED display means the CPU is not starting at all. Can be caused by a myriad of things.
You can start by reseating each of the ROM chips.
It looks like you have an AMI brand CPU chip which is a notoriously suspect manufacturer if indeed that is a 6808 CPU in the socket. I would start by replacing that chip since it is socketed. You could borrow the CPU chip from the sound card as long as it is a 6808 and not also an AMI brand chip.
Some good reading on the steps needed to bullet proof your boards. https://pinside.com/pinball/forum/topic/vids-guide-to-bulletproofing-williams-system-6/page/18#post-5597994
Newcastle, OK
