Apple IIgs not moving drive heads - IWM?

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Apple IIgs not moving drive heads - IWM?

Hey, all! New here, looking for some advice.

I have a IIgs that doesn't like reading 5.25" disks (and no 3.5" to test). The 5.25" drive works fine in a IIe with a newer controller with the DB19 port. In the IIgs, the drive head doesn't seem to like to move forward, so formats fail, reads fail, writes fail as soon as that head needs to move. Not knowing much, I assume that something is up with PH0-3, as those seem to control the drive head.

On boot, PH0, 1, and 2 will show the same thing on the oscilloscope, but PH3 is dead. On the IIe, all 4 lines show the same thing. PH3 seems to be the culprit, then. Reading from the IWM directly, pin 27 (PH3) is also dead. My question is -- does that track, or is PH3 normally flat on boot for a IIgs? If it does track, why is only PH3 dead? Is there a spec for the IWM that shows the logic used to light that up, or is my next step just to find another IWM?

Thanks!