I've plugged my sim900a module to a power source of 5v and 2amps. The power led is turned on but the network led isn't. What can be the problem?
A lot of possibilities.. some ideas
- broken module
- poor or broken antenna
- electromagnetic perturbations near the module
- damaged or invalid SIM (does it work in a phone?)
- SIM inserted the wrong way
- PIN code needed for the SIM
- …
Connecting the module to a serial interface and sending AT commands would help you dig into the status
The sin works on the phone, doesn't have a pin either. How will i know for sure that the module is broken?
Use AT commands to see what’s going on
I'm new to Arduino, what's that?
If the network led is not blinking at all, then the module could be in standby state. What type of module is this exactly?
"Full size" UNO shield like the linked picture?
If yes, the power key have to be asserted to start the module.
At first you could press it manually.
what kind of module do you have? did you connect it to your arduino (which one?)?
➜ we need more info. Do yourself a favour and please read How to get the best out of this forum and provide necessary documentation for your ask.
We decided that our module is bad, and just decided to replace the whole module
does not seem very scientific 
The SIM900A-model is locked to these regions:
- China
- India
- Singapore
- Malaysia
- Thailand
- Indonesia
- Cambodia
- Vietnam
- Laos
- Burma
- Brunei
- Philippines
- East Timor
if you are not there, the it won't work. Some users managed to upgrade the firmware apparently (see this)
it would have been better to connect it to a Serial line
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