Unfortunately though I am making progress, I can't say I'm seeing results (yet). I received a Pentium Pro CPU (200MHz, 256kb) - it was cool to handle such a large processor. I have a TR3 system which when putting it together in ~December left quite an impression handling the CPU, yet the PPro almost seems larger and heavier still.
I thought I'd have to wait for RAM until I remembered I had bought this fully populated Compaq server RAM expansion board for cheap on eBay many years ago. It had been sitting wrapped in an antistatic bag all this time; I dug it out and lo and behold, no shortage of 168 pin EDO ECC FPM RAM! I borrowed four identical sticks from it...
So, I populated the CPU board like so... ignoring heat sink for the moment since the case fan blows directly onto the processor when the installed.
And flip the switch... and.... sigh. When powering the machine, little happens... no fan, occasional barely audible click of a relay from somewhere in the system, and a motherboard LED flashing every second. It's the exact same behavior you see on a Deskpro XL if you unplug the fan from the motherboard. So... hmm.
Potential problem areas:
1) CPU could be bad. I have no reason to think this... it looks relatively undamaged, top and bottom, with no bent pins. I really don't want to purchase another.
2) CPU board could be bad... I will unwrap the second one and give it a try. I double checked the SW2 and SW3 configurations per the quick reference guide - they are correct.
3) Could be the RAM I used is not 100% compatible but that should be easy to verify with a couple of other sticks. I am using 4 sticks of 228468-001 from that server RAM board, which appears to be a 32MB EDO ECC 60ns stick. Should be OK?
4) My hunch is that the XL requires the newer system/IO board to use the PPro cards. I wish someone had one of the newer systems & could verify. I do not see a path to sourcing the newer system board.
Finally, regarding the mysterious two connectors on the PPro board, I still don't know what they are, but I noticed Compaq's old memory upgrade reference has this cartoon drawing, almost suggesting a board should be in this location. Mystery!