I have a project in Pakistan, where about 30 environmental monitoring stations are already installed in last 2 months. All these stations are using RUT240 as a mean of data transmission(by FTP via public Internet). I have faced a problem: already 4 routers on different stations are stopped functioning after certain days or weeks of normal operation without any visible reason. All the routers was substituted by our Pakistan partner with new ones. The "faulty" routers was brought to its office where were tested. All the devices seem to be fully functioning, but all of them cannot register to the cellular network (The Status LED are blinking 2G => 3G => 4G and "Denied" in the Operator state field on web-interface).
The SIM (was tested 2 different ones from 2 operators Zong and Ufone) are OK, PIN is disabled, balance is positive.
After that test the same SIM's was inserted into another "new" router of the same model, there was no problem with registering and data transmission..
The configuration of this "new" working router was saved and then uplodated to each of 4 "faulty" routers. The problem was still present. (FW version on "faulty" and "new" ones was 1.07.1). All "faulty" routers was resetted to factory default and configured manually and also using a config file from a "new" router. - NO RESULT. One router was upgraded to the latest version of FW - NO RESULT.
What could be a cause of this problem?
The stations are powererd by the solar power (with 12V lead battery). There were no power problems (the data loggers of all the stations remain active registering the data from the sensors during the router outage period). The stations are rather distant. Nobody has access to the routers remotely or locally before failure..
The troublesooting logs are saved and can be sent on request.