Even if a CD-ROM drive normally requires some non-Apple driver, it should still be able to boot your Mac. It's kind of counter-intuitive. So long as the CD is bootable, it should boot your Mac in nearly any CD-ROM even if sticking it in after it's booted some other way does not produce an icon on the desktop.
It's possible that there is a hardware problem with your hard drive(s) and also there may be a problem with the software on them. It is possible that the same hard drive will work in one Mac and not on the other and for there to still be nothing wrong with the SCSI bus.
I recommend trying other SCSI devices to see if the problem is consistent across all SCSI devices, or only is affected by some of them. If you hook up a SCSI CD-ROM and boot the Mac with it consistently well, I would say there's nothing wrong with your SCSI bus, and your focus should be shifted to the drives themselves. I believe this is the next logical step to take.
The Quadra 700 was built to be an especially durable computer. I don't think it has ANY electrolytic caps on the logic board. I would tend to suspect any other part before the logic board.
You should be able to find a bootable System 7.1 - 8.1 CD image somewhere if you look around. If you burn this with Toast, it should be able to boot your Mac if the SCSI bus is working, regardless of the obscure brand of CD-ROM you may be using.
It's possible that there is a hardware problem with your hard drive(s) and also there may be a problem with the software on them. It is possible that the same hard drive will work in one Mac and not on the other and for there to still be nothing wrong with the SCSI bus.
I recommend trying other SCSI devices to see if the problem is consistent across all SCSI devices, or only is affected by some of them. If you hook up a SCSI CD-ROM and boot the Mac with it consistently well, I would say there's nothing wrong with your SCSI bus, and your focus should be shifted to the drives themselves. I believe this is the next logical step to take.
The Quadra 700 was built to be an especially durable computer. I don't think it has ANY electrolytic caps on the logic board. I would tend to suspect any other part before the logic board.
You should be able to find a bootable System 7.1 - 8.1 CD image somewhere if you look around. If you burn this with Toast, it should be able to boot your Mac if the SCSI bus is working, regardless of the obscure brand of CD-ROM you may be using.