Check page 11 of the manual. It shows blue lines for the routing of the Node board cables. From that diagram, you can see the CPU is wired to Node 10 (4 coil node), then 24 (ecto LCD), then 9 (core node) and lastly, 8 core node).
From this path, we can assume the cable from the CPU to Node 10 (way at the back of the PF) is good. The problem is between Node 10 and the Ecto goggles node. It could be either board or the cable itself. Probably best to try replacing he $3 cable first.