Problem with SIM908-C - NETLIGHT IS ALWAYS ON?

[kafatsi]

Hello everyone,

I am trying to use SIM908 with Arduino, but having problems with it. I used the reference design to create my own, below you will find the schematic. I have a stable 3.6~volt VBAT.

The problem is : the netlight pin is always high, therefore the net status LED is always shining. It should be blinking, but it doesn't. When i press the power button the LED goes off, as soon as i stop pressing it goes on again.

The PWRKEY pin should be internally pulled high as i know (to 3v?) but it is 1.3V, and when the button is pressed it is grounded as it should be.

I am tracing my routes on the PCB but haven't been able to find any short circuits or jumps. What may be the problem? Any help is appreciated. Thank you.



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Also, I have tried connecting a 3.7V li-ion battery directly to the pins, still the same thing (weaker light tho)

One more thing i noticed : the SIM908 chip gets unusually hot, not so much but i don't think it is supposed to be like that.

 

[kafatsi]

Another update:

I have done continuity test for all pins and components, i have found a problem don't know if it is relevant or not, but the GPS_VCC_RF (output 2.8v) pin seems to be unusually connected to the NC pins. I have isolated the traces on the PCB, even let the pin float but still seems connected. I'm guesssing it is an internal problem in the IC. Since it is an ambigious connection to an output pin which is a voltage generator, it may be haywiring all the internal voltages maybe?

Still no help?

 

[matxt]

Hi kafatsi, have you solve this problem? I have the same issue, netlight led is allways on.