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Correct way to remove ST-Link from Nucleo-F401RE, also did I destroy my board...

Question asked by neff.david on Nov 22, 2015
Latest reply on Nov 23, 2015 by Clive One
I prepared the circuit in the attached image and planned to remove the ST-Link part of the board to finish my project.  Before doing this (because I messed it up last time) I checked that I could externally power the board with a 9-volt battery. Before applying the voltage I disconnected from usb power and moved the JP6 jumper from  U5V to E5V. I plugged in the battery and everything worked fine.....but then I decided to change some code.  

I removed the 9-volt, set the jumper back. Then I connected ST-Link to my PC again by usb and now nothing works.  I get a FAIL message in the Nucleo "The interface firmware FAILED to reset/halt the target MCU" and  the ST-Link utility tells me "Cannot read memory! Disable Read Out Protection and retry."

Is one of the boards now bad? Is it in some state that is reversible? What is the best way remove the st-link part of the board?