troubleshooting of produced prototype: nrf9160

[David]

Hello,

I have developed 10pcs of one prototype with the nrf9160 SiP. 

I have some questions regarding some errors im having.

Regarding the SIM 1V8 driver VCC, for UICC interface, I am observing a fluctuation on this channel/voltage, from 0V -> 0.4 VDC, with approximately 1hz frequency.

What can cause this to happend, what is the normal behaviour of this channel when it is short-circuited with ground or something else/similar ?

My second question is regarding the attached image, im observing this on a few of my prototypes, im not able to upload any modem firmware to the SiP, any idea why?

Regards,

David

[David]

Hello,

If I meassure the voltage on some other boards of my prototype, I meassure a stable 2.2V on DEC0, on the one prototype that I am having the issue with the sim-interface voltage, I meassure here between 2.1 and 2.2 VDC, oscillation. 

As I mentioned here first, I have 3 other boards of the same prototype, which does not have the fluctuation on the SIM 1V8 VDD, but on these I meassure 0VDC on SIM-interface VDD.

I am still waiting for the correct capacitor components, for DEC0 -> GND. Therefore, DEC0 is floating at the moment.

I have not tested "shorting the SIM traces past U8", do you mean SIM_IO, SIM_CLK, SIM_RST ?, should I test shorting all these together?

Regards, David