Please let us know how you make out with it! :-) Yeah, that's better than nothing. I just looked over my notes from looking into the CMV-x000, and alas I don't have any useful data to report (yet). That's kind of odd; the top block of results make it look like it's dropping the 0400 bit (e.g. "S/B", which I assume means 'should be', = 161612, and "WAS" = 161212 makes it sound like it dropped the 0400 bit); but the block below makes it look like it's picking that bit (it shows 0 and 0400 under the S/B and WAS columns for that location). Eh, no biggie; clearly the 0400 bit has issues! ;-) Not sure I see that happening? If your CPU is an 11/73 (which can directly 'access' [hate that verbism :-] all of memory from ODT, unlike the 11/23 which is restricted to the bottom 256KB), try playing around with a failing location, and its alternative, directly, and see if a store of random data into one can be read back directly try reading 03561212, etc. Then go back to 03561612 and see if you get 0123456 back when reading it. Etc, etc. That should quickly verify if the problem is just some locations which drop/pick bits, or if there are addressing issues. I looked at my CMV-x000 boards, and on all of them, the chips are soldered in, not socketed (which most of the other ones I looked into had, which made working out the chip<->bit tables very easy - pull random chips, and see what happened :-). But your proposed move should let you identify if you have the right chip. Once done, you might want to check low memory from ODT to make sure you don't have the banks inverted (i.e. what looks like the top bank is not in fact the bottom). It probably wouldn't boot the diagnostics, if so, but it'd nice to find out directly! Please let me know what the layout is, and I'll start the Computer History wiki page for this board with that info. Noel