The main part of the output that you posted is from the system controller (a Linux based appliance that underlies and controls the SPARC machine). The boot up from the SC that you posted finds no hardware errors and says "POST Passed all devices".
My thoughts are that:
1. It could still be a hardware fault but I think that unlikely given the "POST Passed all devices" message.
2. The "Host System has reset" message indicates the start of the SPARC boot process but it's possible that shortly after that console output is switched elsewhere due to a configuration setting on the ALOM.
https://www.unix.com/solaris/228271-alom-console-3.html
Suggest that you check that out first and post back any progress or lack of.