There isnt usually anything visible when its a reversed supply that
has killed a device.
Thanks for that cheerful start

Sure, but that doesnt mean that the electronics isnt dead.
You can get a situation where the leds are fine since they dont care
about a reversed voltage, but what is driving them has got fried.

Yeah may be, but that takes away the blown fuse part out. So may be the
controller board got fried.

Yeah, that's quite likely given that some of the external
cases dont even attempt to regulate the main supply to
the drive, so it gets 12V reversed if you have the head
reversed on the external power pack.

It had a voltage regulator, so I think it was safe that way.

Will go home and do the rest of testing today

Thanks everyone!!