PDP-8/I memory problem

Hi folks, I'm in the process of restoring my 8/I, have run into a little problem with the core memory, and am out of ideas on what to do next. The symptom is that I can deposit into the core memory now (after replacing a few cards and a core plane), but I can only deposit 11 bits; the 12th bit remains 0. If I deposit 7777, I can examine and get 3777. This machine has 8k of core, and the problem is the same in both 4k banks. Here's what I've done so far to try and eliminate / narrow down the problem -- any further suggestions are most welcome! Swapped G228 A36/B36 Swapped G228 B36/B37 Swapped G021 A31/A32 Swapped G221 C37/C38 Swapped G221 D37/D38 Swapped two edge M220's Swapped G624 A38/B38 (The G221 swaps may have been related to an earlier problem, which I've since fixed) None of these swaps yielded any change in the problem... Since it affects both banks, I'm assuming it must be a problem in some common circuitry. Just so as I'm not totally embarrasing myself, the 4000 bit (the LEFT-most bit) is MB00, right, and not MB11? :-) This whole MSB = 0 and LSB = 11 is very confusing :-) Thanks! Cheers, -RK -- Robert Krten, PARSE Software Devices +1 613 599 8316. Realtime Systems Architecture, Consulting and Training at www.parse.com Looking for Digital Equipment Corp. PDP-1 through PDP-15 minicomputers!