Thanks for all the help. It is now booting again.
I figured out a couple of things. You can use a DMD board form an older WPC game in place of A/V board - no sound of course. You can add a Pinsound board to get the sound. For testing I just removed the AV Board and installed the older DMD board. Fortunately I had a splitter from Pinsound for one of the Molex plugs or it might have been a bit trickier.
With the older DMD board connected the CPU board still didn't boot. So I was pretty sure the problem was with the CPU board and not the DMD board.
So I removed the CPU board and took a good look at it, there was no corrosion damage. The wire for the remote battery holder was not nicely soldered, so in case it was shorting something I resoldered it. Tested the CPU still no boot with the AV board connected.
I was considering removing the TTL chips and replacing them, then I though I'll just try reseating all the socketed chips on the CPU. Reseated the chips and tested the CPU and it boots.
I've played a few games and it seems solid. If it happens again I'll reset the chips and test 1 at a time to see which chip is causing the problem and then replace that socket.
Not sure why it would boot under these circumstances without the AV board and not boot with the AV board. Perhaps there was a pin only just making contact and the extra draw from the AV board tipped it into the non-working condition.