While trying to find U34 on the Newton 2100 motherboard, I went into the archives to see if I could see it in the schematic.
This message on NewtonTalk had a link to schematics:
I went through it and found U34 on page 11. Somehow the process of doing so made me look back at the link Frank had shared of some very nice photos of the boards:
It turns out that U34 is on the bottom of the motherboard (where I hadn't even looked yet).
Thanks, again, Frank.