TRB142 and TRB145 are only usable for USB tethering, meaning they have access to 5V power from USB. This 5V power line goes to (at least) the Quectel module. For other components on the PCB, 3.8V power is only present if external 9..24V power supply is connected.
This dual powering arrangement seems unnecessary to me, and I would like to use USB power alone. I tried modify the schematics with a 5V input/3.8V output LDO, but this did not give the wanted result. Seems that I need to use a DC/DC converter to get it working on USB supply alone. Easy enough, as the external power supply current is less than 100 mA.
But the need for an external power supply for an USB-connected router seems like a serious design flop to me. What was the reason behind such a solution?