We observe erratic behavior: random characters, erratic NVRAM configuration change, freezing...

ADDITIONAL INFORMATION:

We have a PCB that works very well with the MT3334SMI. But once we plug the MT3400SMI, it seems to work at first sight, but then we observe an erratic behavior: random characters, erratic NVRAM configuration change, freezing... We have even seen a value of W3 with AT&V, while ATW3 is not possible! At least this made clear the problem is with the modem, not with our software.


RESPONSE:

The MT3400SMI modules require a 3.3V power supply, the MT3334SMI modules require a 5V power supply. This is most likely the source of the trouble. The MT3400SMI modules can be damaged by powering up with a 5V supply.