Here is an interesting piece on the STM :
"• Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02
""Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA.".
The link is at:
file:///C:/Users/Tony/Downloads/Jay%...A302_FINAL.pdf