[jan-jaap]

It's worth knowing that an Onyx2 DG is a combination of a base DG5-2 and optionally some addon board to make it a DG5-8, a DG5-GVO, a DG5-GVO or some other oddball part. The base DG5-2 is rather easy to find and not expensive, the desirable bit here is the TVO option.

Therefore, I wouldn't waste my time and simply get another DG5-2, transplant the TVO option and the metal bits, and be done with it. Chances of fixing anything on one of these without access to SGI internal documentation and diagnostics equipment is near-zero.