HL7810 Not Responding

IoT Modules Legacy HL Series
1

Hello,
I am having problems getting the HL7810 to work after buying a large batch from Digikey.
Previous batches worked with no issues.
I am wondering how to debug these modems. The contract manufacturer did X-ray the modems and all connections were in good condition.
The serial AT command interface gives no activity upon a reset on the RX/TX lines although the VGPIO shows that the modem is ready.
Any possibility to reflash the firmware without access to the AT interface?

Please advise ASAP. Thank you.

2

Do you have the UART0 port?
You can compare if there is output in UART0 port in Ok board and NOK board.

3

Yes thank you. I have activity on UART0. It looks like the updated board revision has some hardware flaw with the AT UART interface.
Thank you for help.