Get a DMM on your power supply and check the voltages.

Those measurements do not look suspicious. Check the parallel port cable from the transformer

Yes I agree. I was looking at those fuses thinking the power was lost with all those solenoid voltage LEDs off, but LED9 is on so the 50VDC is getting to the driver board. The solenoid voltage is switched on later during boot up via a relay for all those other lines out So as you suggested, reseating everything, especially the finicky Prism card is a start,

Is the fan running on top of the CPU? No bulging capacitors on the motherboard?

There is more than one ram slot on my motherboard, although I understand there was more than one version used. I once added ram to see if it would improve anything, but all it did was make the already long self test even longer.

If the problem hasn't been specifically isolated to the motherboard by swapping the Prism or motherboard, then the Prism card could be suspect. While reseating the Prism card often solves issues with communication between the motherboard and the Prism, there's a lot of things that can become a problem on the Prism itself. The Prism sandwich has socketed ROMS that could have chip creep, for example. Mine had broken traces at the connector that had to be jumpered. It's a delicate thing, so be very careful if you need to pry the two halves apart to investigate it.