To refresh my memory, I went back to your original thread, as suggested by Daver2, and saw that you have a (possibly) working RQDX3 board. I'm not about to tell you which puzzles are more interesting than another, or how you should be spending your spare time. But if I were in your position I would be looking at this:
Quick Links Feel free to click on one of the links in this section to jump to the material you are looking for: Introduction Quickstart Guide Floppy Drives Hard Drives M…
avitech.com.au
or perhaps this:
This simple PCB will enable one or two 3.5″ or 5.25″ floppy drives to be directly connected to a PDP-11 RQDX-series controller. It is a simplified version of my earlier RQDX Breakout Bo…
avitech.com.au
There should be enough info there to let you test your RQDX3 with a readily available 3.5" 1.44m or 5.25" 1.2m floppy drive. If it turns out that your RQDX3 is toast, replacements can be had for not a whole lot of money. In any event, with a bit of tinkering you should be able to put something together that would let you boot RT11 or XXDP off of a floppy disk and debug whatever is not quite right with your 11/73. There's a pretty good walk through at those links on the hardware, software, and equipment needed to pull it off. You likely already have the DEC equivalent board needed to interface a floppy with your RQDX3. Getting something workable might be as simple as preparing a disk, hooking up a floppy drive, and booting up.
Be advised that the originator of the site linked to above is a frequent flyer on this site.