Only one Z axis motor is working

[AzaB2C]

@bar

common issue with this batch of boards

Curious if root cause is understood? posted info/questions that may be related at

What can we improve in the hardware?

Are the TMC2209 ENN Pins unconnected and floating? If so, is that intentional because enable/disable happens via UART? Am wondering if this could be causing some boards to have one or both Z stepper motors unexpectedly/randomly not work. Am wondering if people with “bad boards” (that they would normally just trash) and unreliable Z axis behavior, but also have brilliant eyesight, dexterity and a fine tipped soldering iron… might see better behavior if they solder blob the TMC2209 ENN and GND…

Edit:. Saw some posts about a batch of boards not being soldered/reflowed correctly. Saw some people having success fixing by reflowing or hot air gun. But am still curious about ENN pin mentioned in above post.