[johnnym]

Then I downloaded the SXCE build 130 - and surprise - that worked! Through trial and error, I have discerned that the following versions of Solaris boots up successfully (USB vs CD turned out to be a red herring - if the OS boots on CD, it also boots on USB):
  - Boots successfully:
      - All Solaris 10 released before 12/15/2011 (Solaris 10u10 and earlier)
      - SXCE build 130
      - Solaris 11.00
  - Boot Fails:
      - Solaris 10u11
      - Solaris 11.1 and higher

You might also want to give Tribblix a try. I never tried it though, but it might just work.

Apart from that Debian GNU/Linux Sid from Debian Ports (had it running on a T5220 for a while) and OpenBSD should also work on it. And both might allow for LDOM support and configuration. Here's an article for OpenBSD on this regard: https://flak.tedunangst.com/post/OpenBSD-on-a-Sun-T5120

- OBP : OpenBoot 4.28.0

I was not able to successfully google the latest version # for ILOM and Openboot.  I would be very grateful for that info.

Maybe you find it here: https://dogemicrosystems.ca/pub/Sun/Syst...ml#SET5120

The T5120 was already EOL when that System Handbook version was current (in 2011).