An obscure fact: the F2 switches between X and FP sync based on shutter speed. Speeds of 1/125 and up are FP-sync, not X-sync. This is implied, but not literally stated, on the flash sync page of the F2 manual. It's also mentioned here:
http://www.mir.com.my/rb/photography/hardwares/classics/nikonf2/flash/index.htm This is in contrast to the F, where you have to move a little dial inside the speed dial to switch between X, M, and FP.
What this means, and I verified it with my F2, is that you shouldn't see the electronic flash through the shutter at speeds of 1/125 and up, because the camera is triggering the flash just before the shutter opens as if it were an FP-bulb.
That doesn't explain why your camera doesn't fire the flash at the X-sync speed and slower. But at least now you know the PC terminal works; perhaps the problem is internal to the X-sync contacts.