Ed Beeler sent me some spare Star Rider CPU and VGG boards to help get me unblocked. I swapped out the bad CPU board I had with one of his good ones and the game partially boots! It gets as far as the ROM test, at which point it fails all the tests, as if the ROM board is unpowered and/or disconnected. I am out of time tonight to troubleshoot any further, but I did manage to get a video capture of the game booting up this far. NOTE that this is from real hardware, not Daphne or emulation. I used an RGB->s-video convertor board from jrok (as mentioned in a previous blog post) to make this happen.
Looking forward to getting this working fully and then testing it with Dexter rev3!