We prototype with a BG95 M3 module and have problems with a short circuit of the USIM_CLK line. We unsoldered the capacitor and cut open the connection to the SIM card holder to make sure none of these components are the reason for the failure.
I believe because of the short circuit the AT-Commands regarding the APP work fine (for example QPOWD command) but the commands regarding SIM connection (like CMGF, CMGL or CMGD) result in an ERROR - is this assumption right?
Is there any software reason why the CLK line is pulled down to GND - if yes how can I redo this pulldown?
I did a mistake in the layout by connecting the USIM_VDD with a 100nF capacitor to general GND and not to USIM_GND - could this somehow caused the CLK line short circuit?
This failure is on two PCBs out of an order of 5 PCBs so maybe it is an assembly mistake but I want to exclude any reasons. The other PCBs work fine with a resistance of around 55 k Ohm between CLK line and GND does that sound about right?
Thank you very much for any comments and advises to prevent this failure.