Tobias Russell wrote: An X/Y driver failure will typically manifest as a failure of a range in the address space - or more specifically holes throughout the address space corresponding to the matrix size. The failure of a particular bit in the word-width suggests a problem in either the sense or inhibit circuitry of that bit. On the whole, an inhibit driver is more likely to fail than a sense amp, as the inhibit drivers are relatively high-power and may have heat-dissipation issues. You may be able to discern between a sense amp failure and inhibit driver failure by examining some memory locations which you know contained 'data' and have not been accessed since the failure. If you can scan through those locations and find that the bit in question shows variation (both 1's and 0's) on the first examination, but then return all 1's or all 0's on any subsequent examinations through the range, then it suggests the sense circuitry is working but the inhibit ciruitry is failing to restore the bit after the destructive read. (Of course, if the machine did a full memory test/scan at power-up the above is not going to help.) (If it might help, see http://www.cs.ubc.ca/~hilpert/e/coremem/index.html for (my own) treatise on the organisation and principles of operation of core memory.)