>>> The obvious answer is bad memory. >> >> At the board level, yes. Deeper, it could be bad memory bits or bad >> memory decode. > > Yes, one of the standard early PDP-11 memory tests is the "no duplicate > address test".
I should say that the memory board is not _completely_ whack -- it is passing the rather thorough MAINDEC ZQMC, a 0-124k exerciser with multiple pattern/sequence tests which also kicks around the KT11. That doesn't rule out the possibility that there is a lurker in there not covered by the DEC diags. But if there is, its something subtle...
