Re: disconnecting SCSI and trying the floppy alone, I believe what you are proposing is a sound experiment: try it. Most 68K Macs will show the blinking question mark floppy icon if the floppy drive is empty, and will try to boot from the floppy disk alone if you have a valid one inserted for your particular model. What I find appealing is that you can easily try it repeatedly under a wide variety of situations, from a cold start, many consecutive times, and after sitting on for hours, and the behavior should be identical each trial if the motherboard and power supply are good. If you get discrepant behavior on power ups, there are fewer suspects. You can also try with no floppy drive, and look for consistency, and try a hard drive boot up, no CDROM connected, and without the floppy drive connected.