I just noticed one more thing about the FDR traces of the trim commands. MCAS trim commands show up in the trace even when the cutout switches are used. But that command doesn't reach the motor, and the stabilizer angle remains the same. This suggests the automatic trim commands are sent to the FDR to be logged directly by the FCC, and are not measured somewhere between the cutout switches and the motor, because if they did they wouldn't show in the FDR trace.
However this doesn't seem to be the case for the control column trim switches. In the FDR trace from 05:40:40 to 05:43:05 there are no recorded pilot trim commands. However, in this interval there was this discussion between the pilots:
"At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working."
This suggests the pilots tried to use the trim switches, but it didn't work and the command doesn't show in the FDR trace. If that's the case, it means the information about the thumb switch commands is recorded by the FDR from somewhere between the cutout switches and the motor.
Unfortunately I wasn't able a lot of information about that motor, except this document, previously referenced in the initial Ethiopian thread:
http://www.eaton.eu/ecm/idcplg?IdcService=GET_FILE&allowInterrupt=1&RevisionSelectio nMethod=LatestReleased&noSaveAs=0&Rendition=Primary&dDocName =PCT_3401314
It has information about some circuit board fixes for the two versions of the motor used on the NG. That issue didn't affect the MAX version of the motor according to the document. According to that document the part number for the motor used on the MAX is 6355D0001-01, but unfortunately I haven't been able to find any schematics for it.
In any case, that "motor" is not just some dumb piece of hardware, since the issue fixed for the two NG versions is "Solder joint fatigue of the memory chip". A dumb motor wouldn't have a memory chip. It's quite likely the motor is designed to communicate with the FDR, so it's possible the pilot trim commands are logged to the FDR by the motor.
Later edit: actually I see yoko1 found some schematics two days ago on post number #782:
MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Unfortunately, as he concluded, the interesting stuff happens inside the "controller" part of the "motor", for which we don't have a schematic:
