Update: After removing all the boards, checking jumper settings, etc. and reinstalling everything again. I am please to announce some progress. The PDP-11/23 now boots up to the diagnostic monitor. Thanks very much to people who replied with technical help and particularly to Glen Slick who helped with board identification and configuration and help me fix the QBUS slot assignments. The original slot assignments were wrong and the bus termination was not at the end of the QBUS. The current slot assignments are: Row 1: AB - M8186, CD - 256KB memory Row 2: AB - DSD disk interface, CD - grant continuity Row 3: AB - M8028 DLV11-F async interface / console port Row 4: <empty> Row 5: <empty> Row 6: <empty> Row 7: AB - M8016 KPV11 power fail / line clock Row 8: <empty> Row 9: ABCD - M8012 BDV11 diag ROM / QBUS termination I have added a few pictures here: http://sierracircuitdesign.ddns.net/temp/pdp11/ Next Steps 1) Find the manual for the diagnostic monitor to figure out how to run some test. 2) Locate some 8" floppies with RT-11 loaded and connect the floppy drive