AT&T 3b1/Unix PC Floppy controller help

I'm working on one of these systems, and have run across a floppy controller issue. Everything else in the system is functioning fine, including booting from HDD. However, I have a problem where the floppy drive has power, physically works, and connected properly etc, but what I find is the drive/controller will recognize a disk is put in, click, then nothing. Just due to the way I'm working on this, I haven't been able to test any signals at the controller IC (WD2797), but I have completely swapped the IC with a different one just to check. Now, the question is, without looking at signals, what is the probability the lack of any action is could be a problem with the input to the IC (write, ready, track0, index, write protect, density signals) or with the output signals (step, direction, DRQ IRQ)? There are tri-state buffers (74LS244-input side, 74LS240-output side) on these signals, and I'm thinking one of these are misbehaving, but trying to determine which. Or could it be something completely different? Or any good suggestions on troubleshooting this?