Further PDP-11/05 debugging -- core memory faults

Hi all -- The CPU in the 11/05 seems to be behaving nicely as far as I can tell, now that the Microcode ROMs are no longer filled with bogus data. It will run small programs I've toggled in without issue, and so I've moved on to testing the memory. Basic testing (via the simple address test listed here: http://www.psych.usyd.edu.au/pdp-11/hints.html) reveals that most of the 8KW of core (H215) and controller is working pretty well, except for a 128 byte range between 012000(8) and 012200(8). Within this range, all words read back as all zeros regardless of what is written. Given the nature of the fault, I tend to think that this is not an addressing problem or an issue with the core drivers -- if it was any of these I'd expect the fault to repeat across the memory space in a pattern, rather than being isolated to a single contiguous block of memory. If that's true, then it seems that the core plane itself might be at fault. Which doesn't surprise me, I'm actually surprised it works at all -- when the /05 arrived the H215 core memory board was loose, banging around inside the chassis. Does my initial analysis seem reasonable? Anyone have any experience debugging one of these and have any tips to share? Thanks, Josh