Seems to come down to increasingly intricate work, with a large Luck-factor, once the outboard electronics is (presumed) vetted. As nobody publishes the schematics for such proprietary (and ever-altering) boards: makes it hard to (see where to) measure the resistance of the coil driving the head positioner (not to mention: look for Opens in the/a head-coil(s) -- though that's irrelevant if the suckers cannot be moved in the first place.)

As to making a mini- clean-enough room via big plastic bag and a through-flow of some clean bottled gas: you'd hope to find that the head-positioner is connected by a mylar strap-with-traces: into a soft elastomer? receiving jack. And it has just come loose. Odds?

Anyway, what's to lose? I suppose I'd want to take a peek inside, once all imaginable outside tests have revealed nada. Gas bottle + regulator (on loan?) with carefully air-blasted-off surgeon gloves -- could get you a reasonable probability that any micro-contaminants would not destroy things in the time span to dump the data (?) Can't see such a venture needing hours and hours.. which is a +
('Clean'-rooms are, in the end: merely 'clean-enough'. That Questar telescope cleaning was probably the closest I've 'seen' to Perfection in that arena.)

And, at least from Inside: you could measure the resistance of that driver coil; perhaps see why you don't hear head action.. perhaps even see a broken *teensy lead-in wire? You Can run the drive with top off and see exactly what isn't happening -- saw this under Plexiglass at a show or two. Highly-unlikely your new/used controller board would have an identical failure to present one, eh?

* there is (somewhere!) silver-bearing conductive epoxies (or similar) which could repair such jeweler-level wire-sizes, though the Formvar(?) insulation would need a drop of the magic solvent for that: also Out There.) Without a micro-soldering station to-hand.. well, you Know.

(I have, through the years (with/without assistance) embarked on such improbable projects.. usually because The Machine was down and, you do what you Have To.)
Watched true Maestros, too -- for tips on not over-doing! These were not all fools' errands and it feels rilly Good to beat the odds.


Luck!

moi


PS - as to Doze not seeing it.. I would imagine that, sans actual head-positioning feedback to the firmware, there would be some equivalent to a 'POK'? POST [negative] etc. which would then fail to tell the outside world that it's ready for business. No? So a broken/detached wire likely would do just what you see. WAG, etc.

Indeed, it appears that this TVS did exactly what it was supposed to do -- die First before all the other stuff Would! (Forgot you had er, REVERSED POLARITY as in, bad-Scott.) I've learned to look always at that 'little-tent' in the Molexes. Too lazy to troubleshoot the consequences.

Concur re ever trusting the thing again.. with $/TB decreasing as we speak, it isn't even worth My time to futz with the stuff I was suggesting, except: data recovery doesn't care about practicality.
(Maybe the dead-short failure-mode is also intentional? All switchers would shut-down for that - right?)

Info == power! You got the exact component without a tedious tracing sans schematic.
(But I think it would have been more Fun.. had it been a fixable 'Open' inside!)

Could the Why of the new board's failure to communicate -- be a firmware thing? Go to all that trouble and find ... you have to match some firmware to a specific run of drives, etc. == bummer.

Congrats on Success!


I.