I am using the m66 module.
Although I use three gsm modules, it does not work at all.
I noticed that there is no power even though sim vdd is connected.
why sim vdd is not powered even though it is powered.
You have changed the three modules and all of them have this kind of situation. It is suspected that there is something wrong with the SIM card. Have you changed the SIM card and tried again?
You can use the following AT Command to try, SIM card normally output as follows: