06 August, 2015

Fixing modem detection problems on MPR-L8 or A5-V11 mini 3G routers

If you have one of these modems you may have encountered the problem, that on first try your USB 3G modem is working very well, and later it is not working at all. In this post I will explain a very easy trick, on how to fix this issue.

This trick is for the original firmware and for these two devices:

I have experienced this problem with the ZTE MF680 and ZTE MF110 modems, may be the problem is the same for other modems.

The reason behind this behavior is that these modems after powering on or plugging in, need a mode change from USB storage (this is used to install the Windows driver) to USB serial modem mode. On the very first connection this is working without any problem, but then the router stores the USB device type in the non-volatile RAM and upon next power on or plugging in the modem it is not doing the switching.

The solution is very easy, if your modem is not detected, unplug it, plug in an ordinary pendrive, then unplug the pendrive  and plug in the modem again. Now the modem will detected correctly and switched over to serial modem mode.

This router, with the original firmware doesn't support LTE (4G) modems, at least not those which are attempting to connected as USB network adapter (e.g. ZTE MF821D).

Here are some screenshoots about what you see in the different situations:

In this screenshoot above on the top right corner above the version number you can see, that the antenna signal is crossed, this means that the modem is not detected. In the bottom in the 3G Module section you can see, that it is detected as a 3G Device, but from the VID/PID (Vendor/Product ID) you can see that is is still in USB storage mode.

It is normal, if this happens for 1 or 2 minutes after switching on the modem, but if it is not changing, then you should do the pendrive trick.

Here with the pendrive plugged in, of course there is no radio signal and you can also see in the bottom, that this is correctly detected as an USB Disk.

Now after plugging back the modem, for the first minute, you will see the same situation as on the first screenshoot, but after approximately one more minute the VID/PID will change (in my case it says that it is a Usb Disk which may to the SD card reader in the modem) and again after some time the signal strength display appears. Now the modem is ready to be used.