Connectors in the correct spots and facing the right direction ? Ribbon cables on red strip pin one both ends and not off by a row ?

LTG : )

If you disconnect ALL ribbon cables from the MPU, does the board boot up?

Did you get out the multimeter set to continuity and verify that all the traces coming out of the chip socket have continuity to where they're going on the board? Sometimes a trace problem isn't visually obvious. Check the continuity of each pin, front and back of the board.

It really seems like you have a ribbon cable connecting the CPU board damaged, backwards or off by one row.

Have you tried disconnecting ALL the ribbon cables and switch matrix connectors from the CPU board (leaving the power cables plugged in) and powering on? Does D19 stay on in that condition? If NOT, then power off and connect one ribbon cable at a time and power on, then repeat this (off, plug, on) with each cable until you see which one is the issue. Once all ribbon cables are in, if you haven't found the problem, continue with the switch matrix connectors, one at a time with each power cycle.

If that doesn't work:
With power OFF can you press on the ASIC chip firmly then try booting?

If that doesn't work:
Can you post pics of each side of the board you put back in so I can see the connectors?

Also, I assume you didn't keep the original RAM to put back in to the new socket and remove the possibility of a bad NVRAM chip?

Re-reading this, did you check continuity on the NVRAM chip or on the NVRAM chip SOCKET on the CPU board? You need to check the socket with no chip in it.

You basically need to remove the NVRAM chip, then check the socket on the CPU board, front and back.

For these first two, you want NO CONTINUITY to come up:

(Powered off) First check the back because there's some questionable soldering. It looks like one or more may be shorted with solder touching. (Continuity mode on multimeter) Put one lead on the first pin, then the other lead on the pin next to it. UNLESS the traces on the board are connected, you should get NO continuity with adjacent pins. Walk the multimeter down checking all adjacent pins to make sure they aren't shorted together on the backof the board. If they ARE shorted, clean up the solder causing the short.

If you get through all the back ones and none are shorted, then flip it over and check adjacent pins on the front of the board by sticking probes in each adjacent socket connecter.

For these you WANT CONTINUITY to show up for each pin.
If you get through that with no shorts, put one end in the first socket connector and the other end on the first point that the trace on the CPU board coming from that socket pin connector goes to on the CPU board. Then repeat for all of them, going in order down each row so you don't lose your place. There should be continuity for ALL the connectors on the socket. If they all do, replace the NVRAM chip.

Also, did you remove the Game ROM in this process? Check for bent pins on that.

Roadshow Board (resized).jpg

Did you solve the problem?