according to this post:
https://groups.google.com/d/msg/comp.sys.ibm.sys3x.misc/1ddizEn8TXU/wAVIybn…
Quote:"o.k. on a 5363, a C972 is an IPL disk adapter card failed.
There is a 60% probability that it is the disk adapter card (could just be a
reseat of cable J26 and J27) or 30% it is the disk drive or 5 % chance it is
the cable asm. (according to the IBM S/36 5363 System Unit SRC book) "