I started by probing the bad readback reported by Jenne per FRS11582 and  WP7853  on filter 3 of AS_B_RF45.  After ruling out the AcroMag, I pushed on to the Whitening Chassis S1101585 in ISC-R3 near HAM6.  I secured the chassis and retreated to the EE Lab to perform a system check.  This check determined that we had a bad IC.  I replaced the IC, reinstalled the chassis, and the readback works correctly now.

I continued on to the next objective, and investigated EtherCAT Corner 5 per FRS11525 and WP7844.  Time was running short.  After testing I found that the Beckhoff module was working properly, and the problem must originate upstream of the chassis.  The offset was traced back to the CM Summing Node on ISC-R4, and then ... I was out of time and the final objective was not reached.  But we survived another maintenance day.