[ltp] Replacing the Ericsson 3G modem in an X301 with a Sierra Wireless LTE modem

[Bjørn Mork]

I've been looking for a new thinkpad with LTE builtin ever since I got
an external USB LTE blob. That's nothing for me.  Already broken off one
modem USB connector by dropping the laptop om the floor with the modem
attached.  Fortunately the port survived.  Yes, I know I shouldn't drop
laptops on the floor with or without USB gizmos attached. but...

Anyway, I got hold of a Sierra Wireless MC7710 mini-PCIe module.  "Not
for laptops".  OK, it is meant for embedded systems but that's not going
to stop me.  It's just a standard USB mini-PCIe card with the same SIM
slot requirements as the Ericsson F3507g modem the X301 came with.

Let me use the opportunity to thank Lenovo for inheriting a couple of
things from IBM: Really nice service manuals and a design with service
in mind.

Lenovo even were so kind they put 6 antennas in this laptop.  3 are used
by the wlan card, 2 are used by the Ericsson modem and 1 is spare
(probably meant for the Wireless USB option I don't have).  But this
means that I have 3 antennas available for the new modem.  1 for GPS, 1
for TX/RX and one for RX diversity.  Although the latter is optional I
assume it will improve reception a lot in difficult areas.

Back to the easy service.  Removing the keyboard to access the wwan slot
is just 2 screws.  Disconnecting the two antenna cables and replacing
the modem is 2 more screws.  Finding the spare antenna cable is two more
screws.  It was routed past the modem through a hole and taped between
the two RAM slots next to the wlan and (empty) wusb slot.  Pulling it
through the hole and connecting it to the modem was no problem at all.

Reattached the keyboard and powered on, and then all my satisfaction
with Lenovo/IBM just instantly disappeared...  I had heard about
problems with replacing wlan cards in Thinkpads, but had just ignored
that.  It's just a bloody USB stick in an mini-PCIe form factor.  Why
should that be more of a problem than any externally connected USB
modem?  Well, it is. This slot has its USB device whitelist just like
the wlan slot has its PCIe device whitelist, and I got the infamous

 "Error 1804 - Unauthorized WAN card is plugged in. Power off and remove
  the WAN card." 

No ESC to continue, typing "I AGREE TO VOID MY WARRANTY", disabling the
card or anything else remotely reasonable.  "Remove".  Right.  Thank you
IBM for that inheritance.

Googling led me to this method: http://art.ified.ca/?page_id=218
I did most steps on another PC with Windows, but used the PHLASH16.EXE
program on the Lenovo CD to do the flashing as I don't have Windows on
my Thinkpad.  Other than that, the recipe worked just fine.

But do consider the warnings if you want to try yourself!

After that the X301 booted just fine with the Sierra modem, and I do now
have a Thinkpad with LTE builtin :-)


The antennas seem to work just find for the LTE bands.  Getting quite
good values (this is in my home while writing this):

at!gstatus?                                                                             
!GSTATUS: 
Current Time:  8609             Temperature: 41
Bootup Time:   1                Mode:        ONLINE         
System mode:   LTE              PS state:    Attached     
LTE band:      B7               LTE bw:      20 MHz  
LTE Rx chan:   3050             LTE Tx chan: 21050
EMM state:     Registered       Normal Service 
EMM connection:RRC Connected  

RSSI (dBm):    -74              Tx Power:    6
RSRP (dBm):    -101             TAC:         78B5 (30901)
RSRQ (dB):     -5               Cell ID:     0103B200 (17019392)
SINR (dB):     21.0


OK





Bjørn