nrf9161 custom board - sim card problems - CEREG:90

[RicPT]

Hi.

I have a custom board with a NRF9161. The nrf91's LTE block connects to the sim holder through a NX3DV2567HR switch and an TPD3F303DQDR ESD protection. 

I'm using a very simple firmware just to confirm if all is working but I always get a "CEREG:90" response. 

I've checked with an oscilloscope that the nrf9161 is sending the SIM_CLK signal at the beginning of the connection, but I never see any changes in the SIM_VCC pin (always at 0V). A stable 1.8V bus is feeding the VDD_GPIO. I've made this test in two different boards and got the same result.

Can anyone suggest any good strategy to debug and solve this?

Thank you all in advance.  

[RicPT]

Hi Asbjørn,

I’m sorry for the late reply; I was out for a few days and then working on other things and this matter got paused  My answers are inline:

 

the absence of voltage from the SIM_VDD output on the nRF9161 for your SIM_1V8 input for the NXP chip indicates that there might be something wrong before that location. 

Do you happen to have a nRF9161 DK available? Does your FW and modem FW work on that kit?

- Yes, i have tried the firmware in the DK (with the same updated Modem Firmware) and I get the 1.8V .

How was the nRF9161 SiP soldered to your custom board?

-Manually, using a hot bed. I can accept that could be a bad solder on this specific pin but I get the same reaction in the second board.

How close to the nRF9161 on your custom board are you able to probe with the scope you have?

• I have the track and a via ~ 1mm away from the nrf9161. I’m only unable to test under the nrf9161 but I’m very close to the pin.

Are you able to find the SIM_VDD output pin from the SiP and probe on that to see if there's some slight changes to the voltage at startup that might indicate that there is a short under the SiP?

• I’ve had the Oscilloscope there and can’t find any fluctuations (even very small) even at startup. I have tested the firmware on a second custom board as I think I’ve said before but I haven’t tested this oscillation in that second one.

 The same probing could be done on all the SIM  intercae pins as close to the nRF9161 as possible during satrtup and during enabling of the SIM interface to see if there as some very short signals or behaviour on them.

• I’ve checked the clock signal and is ok, but I haven’t checked the remaining. I will test that.

Regarding the modem FW and SDK version? Are you able to build an example with a later version of NCS and try it on your board to see if that makes a differenc in your case. I'm not aware of any changes to the SDK that would do this, but you never know in some instances.

- This I still need to try this as i will have to adapt the board definitions (2.6.1 -> 2.80 version).

Regards,

[mathiaso]

Hi, Ricardo.

Apologies for the delayed response here. Asbjørn is currently out of office due to the holidays.

Would you be able to upload a PDF containing your entire schematic and the Gerber files so we can have a look at your layout as well?

Best regards,
Mathias