Just when you thought your disk was dead

[Mabry Tyson <TYSON@warbucks.ai.sri.com>]

Beware failures of the proms on the IO board.  We just had a case where one
of our machines seemed to lose its disk.  We swapped in new IO and IO
paddle cards and the disk was still dead.  Bad disk?  No, the fault was in
the proms that are moved from the old IO board to the replacement IO board.
At least one mode of failure for those proms (PLAs?) is that you can't talk
to the disk.  Bringing in 100 new IO cards or disks still won't make it work.

The machine that died last had its IO card replaced in July.  It died while
running normally.