We have around 100 terminals that use EC-25 Mini PCIe module for comms.
- Some of them works flawlessly
- Some will drop offline here and there that can resume connection randomly or by rebooting or by re-inserting sim card
- A few that never connects
The issue is pretty much same as described in Quectel EC25 Mini PCIe USIM detection problem (USIM_VDD=0V)
AT log will show CME error 10, basically can’t find sim card
The Usim VDD is 0V on faulty ones, 1.8v on good ones
On a closer look on the PCB, the 15K pull-up resistor between USIM-VDD and USIM-DATA is not soldered on. There’s no sim detection circuit or code, it’s just 6pin sim connector.
However, comparing the sim circuit from another terminal manufacture who also uses EC-25 with 8pin sim tray and sim detection, the 2nd manufature also left out the 15K pull up.
The resistor in question shown below
My question is that would this explain the cause of some terminals not detecting sim cards? I can’t find any documents substainciating the backend logics of this 15K resistor apart it’s a pull up
On a side note, I have been dealing with this “dropout” issue for over a year now, started thinking its issue with the SIM cards or the tray connector, but increasingly confident that this issue has nothing to do with loose connections, but rather circuit charactoristics of indivisual PCB & its components.
I have for many times seen the connection resumes with
- commandline reboot - not touching anything no chance of virbation
- swapping EC-25 and terminal combination