Hello,
We are currently using your EC21-E module in one of our products.
We are seeing an increasing number of returned items for repair where the failure is down to the EC21-E module.
In our design the EC21-E is controlled via USB using a STM Microprocessor. The failure symptom is the EC21-E fails to respond to AT commands sent by the STM.
If we connect a failed EC21-E directly to a PC via USB, the modem will enumerate. We can open a comm port and send AT commands and get responses. However the failed modems seem to take much longer to enumerate than a working unit. Also the failed modems never register to a network (AT+CREG?) and always show 99 as a signal strength to (AT+CSQ). The failed modem will also stop communicating via USB randomly it seems.
All the modems we have looked at so far have had firmware EC21EFAR06A01M4G installed. We have updated 3 failed modems with the latest firmware EC21EFAR06A06M4G which appears to have made no improvement.
We are concerned we are not seeing any signal on the failing modems, whereas with the same setup, we successfully register with a working modem.
Is there anything you can suggest that will help progress our investigation?
Regards,