SIM7600 with arduino uno

I am using the Arduin uno to send and receive SMS's.

I used the SIM900 platform before and that is working fine

I am using the onboard LED (pin 13) to signal a good network connetion

I am now trying to get the 4G shield (SIM7600)  to do the same.

I had to change the speed from 115200 to 19200 to get it to work correctly.

My problem is:

– everything works fine as long as the USB cable to the PC is connected!!!!

– When  disconnect the USB (after uploading the sketch) – the shield is still conneted to a stable 12volt supply (1200 mA)– The Power LED is ON, the net LED flikkers but I never get the GSM OK LED to light on!!!. And the unit does not respons to any incomming SMS's

 

Changed UNO board, changed power supply but no results