Yeh this is pretty much the way of the world... have two logic boards, an a 64Mb R7000? Mac Edition and a 16Mb Rage128 that is a stock Yosemite/Yikes video card, and a generic Phillips 17" CRT and a Graphite 17" Studio Display (Yikes/Sawtooth era so should be compatible with at least the stock Yikes card) and both cards work perfectly in my Yikes with both displays. But any one of the above combinations isnt working after the initial bong even with all other cards removed.
Have had the CPU and graphics cards in and out a squillion times and made tripley sure they were seated correctly, even played with the position in which the graphics card sits in the slots, which I read on here worked for somebody ages ago with a troublesome 9600.
Have tried various combinations of RAM, and run randomly selected pairs and even singular sticks to no avail.
Reset cuda a few times now with PRAM battery out and power off... even to the point of resetting it every time I changed hardware configurations. No dice.
Even tried the On-Off-On trick a few times that seems to work for some people with glitchy 9xxx-series machines but no difference.
It is always possible that both boards are faulty but this seems a stretch... I am inclined to start suspecting PSU but then again who knows? I presume there is no other PSU that is a direct plug and play with regards to pinouts and plug configuration? I have various 7xxx series machines that work but I have this suspicion that the power supply of the 9600 has a bit more to it.