PDP-11/45 RSTS/E boot problem

Thanks for the pointers, Will; I found the articles practical and useful. I have posted the latest version of my diagnostic over on my project blog at fritzm.github.io. The latest news is that I did repairs on all the implicated DRAMs on my MS11-L, and now both my diagnostics and MAINDEC ZQMC are passing consistently. I am also now able to successfully run the heavyweight KT11-C exerciser MAINDEC. There is a lingering issue with parity abort handling -- it looks as if my 11/45 is a very early model and as such my CPU boards are early etches and apparently have not had all ECO's applied relating to parity. My CPU hardware will console halt on UNIBUS parity error, rather than trap to 114. So MAINDECs etc that check for this trap fail (halt) on my machine. Well anyway, after all this, I still have the exact same failure mode with *both* RSTS/E and V6 Unix! Sad panda... I don't think this is directly related to the parity abort issue, since Noel informs me that V6 Unix doesn't care at all, and I can also see under both OS's that after the recent repairs no parity faults are occurring on the MS11 (it has an LED for that). The KT11 seems really solid now, too. But I suppose it could be some other early-CPU incompato? I think this means I have to go back to working the problem from the other end -- analyze the core/crash files for clues on exactly what it going wrong. Paul: I'll see about retrieving a crash file from RSTS, now that I've cleaned up the memory system issues. cheers, --FritzM.