PDP-8/E MM8EJ G233 Troubles

Hi all, Recently, my PDP-8/E has been acting funny. I finally had some time tonight to run a memory test and found that all addresses matching the pattern XX5XX read back all zeros. Everything else tests fine. I swapped the XY driver board (G233) and found that the problem went away. I can't seem to locate a schematic online. My PDP-8/E preliminary maintenance manual only describes the G227, for the 4k core board. Can anyone help with a schematic, or judging from the symptom, point me to a particular area on the board? I've got a 'scope and should be able to diagnose it if I know where to start looking. Thanks, Kyle ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2012.0.2247 / Virus Database: 3681/6511 - Release Date: 01/17/14