Here are a few pics from the effort. I replaced a bunch of the chips hoping to get lucky. Fortunately, those are cheap and easy. As pickle9000 suggested, I put all of them in sockets except for the RS485 drivers. It reminded me of how much I hate through hole boards. Most of my own PCB's don't have a single hole expect for vias. Super easy to replace parts compared to these things.
The failure was not obvious to me because the symptoms were that some thing sort of worked. It seemed like maybe some sort of software related corruption.
Started with the RAM chips....being careful to get clean holes and not lift any pads.
Here you can see some of the new chips in sockets. The RS485 drivers are the 8pin DIPs next to the DB9 connector.
PC layout. Single board computer on a backplane with ISA slots on one side and PCI on the other.
The bad connection from the SBC to the backplane created a fault with the PCI USB card, the ISA bus, and the on-board network interface which is also on the PCI bus.
And yes, I have a verified working spare vision card. I also have an option to buy a spare SBC with processor and RAM rather cheap. Right now, the HDD is being cloned and imaged. Converting to SSD for main drive as well so I should have some options if things get crazy in the future.
Well done! If I had a dollar for every complex fault that had a simple fix (or the cause was yelling out at me to be fixed) I'd be a rich (OK, less poor) man!