HOW TO - Connect the serial console

[aivanise]

I've bought a ch340 uart converter from pine shop, it looks exactly like the one on the picture. But when I put the yellow jumper on 3v3, i get nothing in dmesg, only when I put the jumper on 5V I get USB device recognized in dmesg and the ttyUSB port is there, but then,, of course, I don't get anything on it since it is on 5V

This is on 5V
# dmesg | tail -f
[98293.116166] usb 3-1: new full-speed USB device number 3 using uhci_hcd
[98293.304184] usb 3-1: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.54
[98293.304187] usb 3-1: New USB device strings: Mfr=0, Product=2, SerialNumber=0
[98293.304190] usb 3-1: Product: USB2.0-Serial
[98293.307329] ch341 3-1:1.0: ch341-uart converter detected
[98293.314267] usb 3-1: ch341-uart converter now attached to ttyUSB0

this is on 3V3
(...)
nothing, nada, zilch

any ideas? is my ch341 dead? My PC too old?