... serious power loss ... or PSU with "bad" ground potential causes high current and EMI across the USB cable shielding ... or ...
Measure the +5V and/or power drain of your support with and without stepper connected ...
Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [
reprap.org] -- Deutsche Facebook-Gruppe - [
www.facebook.com]
Call for the project "garbage-free seas" - [
reprap.org]