Oversized HDD with Mac IIsi?

[croissantking]

I would try using a 50-pin to 68-pin adapter on the motherboard like this one and a 68-pin ribbon cable with a terminator fitted to the end of it, which most have as standard. This is what worked for me on my IIsi and it would rule out any issues with your adapter, which may well not be providing proper termination.

Edit: oh wait, you say you’ve tried OEM 50-pin Apple branded SCSI drives, and the problem still occurs? Could it be a fuse or something on the motherboard then?

 

[dv-]

A BlueSCSI with active termination works fine, so I guess it's just the hard drive having passive-only termination or maybe the termination resistors are even hosed. Yay, I guess? Ugh. What a slog.