I'm not telling you anything but again if you use an apple branded slo mo drive you have and it works then the yahmaha is the issue. That's the first thing you should do. If everything is good that way then the yahmaha is a non bootable drive.

I mentioned caps because you said it was different every time, a clear indication of instability. Again I am not saying it's an issue just a possibility as all these over a decade old machines are going to fall prey to.

Pram zap and cuda switch if applicable have always been hardware correctors since the beginning.

I mentioned before Apple liked having hardware and software suited to itself. With cd rom toolkit external cd roms were able to be used as you say yours can flawlessly. That never meant it could be used in the older macs. I have every issue of macaddict and I'll look and see what was bootable and not in that machine, but just because it's mac compatible does not mean its mac bootable.

Don't be upset with anyone here. All we can do is systematically hit each hurdle to give ideas on possibilities. I have a 6300 motherboard with a G3 sonnet cache card upgrade and three out of five times it will boot and work fine , but when it errors on start I have to do everything I can to get that sonnet Init to load for it to not to error out and lock up.

Good luck with your endeavor, when I get home from work, if the snow thaws, I'll try a yahmaha drive in mine and see if my machine has the same issue.