Mini Gerbil debugging – no communication with PC software

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Symptom DetailLikely causes and their solutions (in recommended sequence)
Power LED 1 is illuminated, but Comms LED 3 not illuminated. No connection to PC softwareWrong software – Mini Gerbil works with Lightburn. Other software including Laserweb and CNCjs are possible but are unsupported.  Mini Gerbil is not compatible with K40 Whisperer (native bespoke Nano M2 protocol, not G-code)

Incorrect Device selected in Lightburn – select ‘Gerbil STM’. See the MG3 installation video.

Mini Gerbil is used with a USB hub, especially one shared with other peripherals like a USB camera. Plug Mini Gerbil and other USB devices into PC directly, not via a common hub.

The USB cable is power only, it needs to be a USB data cable.  Replace.

Faulty K40 grounding.  See

Missing Windows Driver: Win10 does not require a virtual com port driver however earlier versions of Windows do need a driver.
To identify if the driver is not working properly, check Windows device manager (search for “Device Manager”, right click and open/run it) and look under COM & LPT ports, you should see VCP ST microelectronics icon (MG plugged in, Power on). An exclamation mark indicates that the driver is not working properly. An absent driver means that either the cable/plug/MG board is not working/defective, or you need to install the windows driver (for Window versions before 10). See
Power LED 1 and Comms LED 3 are both illuminated, but connection to PC software is absent of inconsistentThe comms has been established, then lost, probably due to a user action in the PC interface, or due to a loose/faulty USB connection. Note that once the comms connection is established, LED 3 is illuminated, but once the connection is lost, LED 3 is not extinguished.

Faulty USB cable.  Replace.

USB plug is not making proper contact with socket – check for looseness. Use alternative cable.

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