I have been using the Q2686 for a long time and since 2G is still available here (Bulgaria) I still use it. But over the years, I have encountered two problems that I have not been able to solve.
The module operates in start / stop mode. Power on, connect, GPRS connect, communicate, Power off - on every hour. It is managed by our internal OpenAT application and external MCU for power on and power off. It works in this mode for several months or years and at some point it starts showing signal quality + CSQ: 99.99 and never manages to connect to the current operator again (despite power off on cycling every hour). If I insert a SIM card from another operator, the connection is made without any problems. But if I return the old operator, even with another of his cards, the problem remains. It turned out that if I delete everything and reload everything (firmware, user application, user configuration) the problem disappears and the module works smoothly for several months or years until the next time the problem occurs. Not all modules show such a problem but I do not see a pattern. Maybe I notice that it happens in places with poor to medium signal quality.
Again the same mode of operation, the same device, but works with a 1NCE SIM card (1nce.com) without a problem. After a few months (more often than problem 1) it shows a signal + CSQ: 99.99 and there is no connection again. BUT now the above solution to the problem does not work. The solution is different. I move the problematic SIM card to another device (just another instance of the same type of device) and the device works normally with this card. Then I return it to the problematic device and the problem is gone.
I have come to these solutions to the problems empirically. Trial and error.
I would be extremely grateful if any of you have an idea of what causes these problems and how to avoid them.
7.46 was a pretty solid piece of firmware and we had a lot of units in the field running it without any issues.
So the things I would check when you get a unit in this state:
at+cpin? //Check to see if it can still see the SIM card.
at+cops? //Check to see what its search mode is
at+cfun? //Check to see if it has fallen back to low power mode for some reason
at+creg? //Check to see if it has been explicitly rejected by the network
at+wopen? //Is the OpenAT application still running?
at+cops=? //Check to see if it can see any networks (this may take a couple of minutes to return something)
The fact it is coming back with a 99 for the signal strength indicates that it has stopped searching for some reason. Normally even if it had been rejected from the network it would be camped on any network in emergency mode.
@mlw
Thanks for the prompt reply!
SIM card works fine, OpenAT app works fine too. The other things will be checked when I get such a unit.
About problem 2 - I can’t imagine how moving the SIM card to another device and returning back in the first one solves the problem without any other actions. Is there something that the module writes in the SIM card, that could potentialy stop the network searching or registration, and other device removes or changes the same thing and solves the problem? I didn’t mention that the problematic modul has default IMEI 012345678901234.
So there could potentially be a few things that are wrong but to answer the questions.
Moving the SIM card to a different module could cause fields to be re written, nothing would be written to the SIM that would stop it scanning or camping in emergency mode but it could stop it from registering.
Default IMEI numbers can cause problems on networks, some do not like it.
The thing that is puzzling is the fact there is no signal strength, if you have been rejected that is one thing but to have no signal strength, espeically if you have multiple networks around is very odd.