Complex PCB troubleshooting and repair

I have asked this question before but maybe someone has some insights
into the following this time around.

How do you troubleshoot complex CPU boards like late model Midway,
Sega, Namco pcb's that have many custom chips with no data sheets, no
schematics and no known good boards to repair them to. I know about
the Huntron but even if you find a signature that doesn't match it
doesn't mean you have a problem at that point. It could be a point on
the other side of the board that is influencing that node. I was
looking at the ABI equipment but I am skeptical. ABIelectronics.co.uk
has some interesting stuff that claims to handle complex cpu boards.
But other then that I haven't seen much. Anyone know if it can be done
and how to go about it.

Thanks
Russ

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