Note if errors are encountered with the reference disk in the drive they will be identified. See Appendix D for full listing. This is usually a case of non-IBM components added to the system.
Some examples are video adapters, hard drive controllers, and the like.
Also lock-ups are common with some video cards added to the system. For IML systems, a common problem is downlevel reference and diagnostics disks. The current refdisk and diags disk may have been used to update the system partition, but sometimes a outdated file remains. The system then has a mix of old code and new. If everything checks out then no problem.