Just heard back from Phil, it was the motherboard that died. The cost was $750 for the board, $100 for parts, and $48 for labor. I would love to have it fixed but at this point $900 is simply too much to justify repairing an older analog scaler (it does have a digital DVI output, but it doesn't work "across the board" with all displays). I basically wanted to have it fixed so I could have a working unit as a backup, or perhaps sell it, but I don't think I could get $900 out of it.
The Rock HD does a beautiful job scaling, and it gives the user control that I haven't seen matched on any other scaler available so far (zooming in 1% increments, custom aspect ratios in .01 increments, etc.).
But again, $900 is simply too much. I feel sad losing it, but I guess that's life.