Problems with Sierra Wireless EM7305

Bjørn Mork bjorn at
Wed Jul 13 08:20:38 UTC 2016

Harald Jung - ECOS Technology <Harald.Jung at> writes:

> when I try to run the modem with qmi support, nm-applet askes for the
> pin.  The SIM accepts the PIN and after a while the motdem resets
> itself and disappears from the usb bus, to show up after 1-2 seconds
> again.

This is a modem firmware reset/crash which we really cannot influence.

Except: I struggled with something similar recently.  In my case the
modem would work as long as I limited the modem to 3G.  But it would
reset ss soon as it registered in an LTE network.

This turned out to be a simple voltage drop problem.  I used a bad USB
extension cable between the host and the modem, and I guess the voltage
dropped below the brownout reset protection when there was a current
spike .

Don't know it your problem is the same.  But it could certainly be from
the description.  There will be a current spike righth after entering
the PIN since the modem then will enable the radio and start searching
for networks.  So the first you should do is to check cables, connectors
and power supplies. If this is a laptop internal modem, then I guess
your only real option is to try to reseat it.  Possibly after cleaning
the contacts carefully,

Or simply move the modem to another host and see if that helps.  If it
does, then there is a problem wtih the host/socket.  If it doesn't help,
then there might be a modem hardware problem.

> If I do it to often, the Modem changes its product_id to 9040 and has
> only 1 Interface (udev loads qcserial) and only 1 bConfiguration
> Value.

That's the modem bootloader.  Likely an intentional failsafe kicing in
because of the repeated resets.

> And it doesn't work at all, the only thing which helps is to remove all power supply.

The single serial port speaks one or more of a number of obscure
Qualcomm protocols.  It's used for ramdumps, flash upgrades and probably
more.  But ModemManager does not support any of these protocols.

> After that it shows up with the product_id 9041 again.
> Kernel Version is 4.5.7
> When I Try to run the modem in mbim mode, I'll get this messages:

The MBIM failure seems unrelated. It never reaches the point where the
modem searches for networks, so you avoid the reset.


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