Jim, Dave, I believe we're suspecting the LSI AE may be responsible for the intermittent very-high written
amplitude on the media, but we wonder if it might also be something fluctuating inside the write head.
Our best guess is that the AE write driver output current control system is not behaving correctly--
and to see it I think your suggestion to monitor the voltage across the write head over time can work.
Remember we think the writecurrent is normal most of the time, we think it jumps higher only
very rarely and very briefly (maybe a few dozen microseconds every few hours).
But if the problem is that for some reason the write head can change efficiency by itself (and frankly
I don't know if this is even possible), then we may need to monitor the output magnetic flux
from the write head to see the issue.
Since your idea is more straightforward to implement, let's do this first and if intermittent bursts of
very-high writecurrent appears on this failing head (and not on one of the other good heads),
then I think this proves root cause.
As for the alternative plan, I think it's reasonable to re-Mfg the drive and make sure the problem still exists first.
Then if we replace failing Hd#5 on the HSA and repeat this, if the problem goes away, this would suggest a Hd#5 issue.
Otherwise, I think this points to preamp.