M66 keeps shutting down


I have an M66 module which powers on, but shuts down after about 10 seconds. It briefly responds to AT commands while it is powered.

The issue appears to occur when the module attempts to register on the network; by removing either the SIM card or antenna, the module remains powered.

With a SIM card connected, but no antenna, the module remains powered and responds to AT commands. SIM related commands appear to work; for example I can retrieve the IMSI by using the AT+CIMI command.

With the antenna connected, but without a SIM card, the module remains powered and responds to AT commands.

The AT commands are sent from a micro-controller connected to the M66 UART port (pins 17&18).

The ATI command returns the following information:

Revision: M66FBR03A05

Any help or suggestions would be appreciated.

It could be power supply issue. When the module tries to attach to the network, it draws more current - that could lower the supply voltage below the treshold, and power off the module. (I have experienced this with the BC66 module, with a current limited supply).
If you are using a custom PCB, you may have to increase the capacitance values, if you are using an evaluation board, you may use a higher current capability supply.

I’ve fixed it!

Like you suggested, I thought it was related to the power supply, and the current required when joining the network; I had a similar problem a few years ago with a different modem.

I checked this morning and noticed a slight resistance between the +ve Pins on the module and the power supply ~ 1.2ohms.

I was using a short length of (thin) wire to connect the board to the power supply. I’ve replaced the wire, and all appears to be working. Another lesson learnt!

Thanks again,


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