When you say ‘now nothing happens anymore’ do you mean the QMX is now no longer drawing power when you push the encoder button, or is it completely dead.
the USB socket on the circuit diagram is J201 and the two USB data lines feed directly into the processor, there is no additional circuitry. As others have said the VBus from the computer side of the QMX is not connected, only the data lines.
If the QMX still shows a current draw when you push the encoder, plug the usb cable from the QMX into your computer, before you try to power up the QMX, then once connected try to power up the QMX.
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If the QMX is completely dead, you need to start looking at the power on arrangement, note that while in Bootloader mode the SMPS are not enabled, only the linear 3.3V regulator is used to power the CPU.
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There is an explanation in the wiki.
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73 Nick G0OQK
