I've dissected my Smart Bro (Huawei E1553) modem for the sake of this mod. Anyway, these USB dongles are relatively cheap nowadays. AFAIK, pcie-mini card-type modems cost 3-4 times more compared to usb-types. Before doing the actual mod, I was still not sure whether this will work on 3.3V supply instead of the common 5V of USB ports. Since I cannot find its electrical specs, I just test it on actual. And, fortunately, it works!
I'm using pins 36 and 38 of PCIE mini card connector for the USB functionality of this port. And for the USB supply, I tapped 3.3V and GND on capacitor C236.This 3.3V supply for the pcie-mini card is automatically turned off during system standby.
There's also a disable pin function for the host to disable the pcie-mini card. It is W_DISABLE# on pin 20. It is held low during boot up of the unit. Also during boot-up, the BIOS will check if there's a load on the pcie-mini's 3V3 output. If it doesn't see any load on the 3V3 bus, the unit will cut-off the 3.3V supply all throughout. Therefor, pressing Fn+F10 keys combination without "load" on the 3V3 will not cause this pin to go to logic high. For now, I'm not utilizing this pin since my "enable circuit" is not yet working. The enable circuit is basically using a p-channel mosfet, which is the same with the bluetooth mod. However, the mosfet I currently have doesn't operate well with only -3.3V Vgs (i.e. doesn't turn on properly). BTW, the enable logic for this pin 20 is opposite of what the previous mod have. Meaning, low (0V) on pin 20 corresponds to "module disabled", and high (3.3V) is "enabled".
I was also got bothered of whether the internal antenna of the modem may not be able to get a good signal strength since Wind12 chassis has metal backbones and the plastic cover itself has conductive coatings. But, there was a U210-lite user who ask me to solder his usb hsdpa modem inside his unit. And I'm quite satisfied with the result even if we didn't wire and reposition the antenna of his modem.
I managed to get coaxial wires (hoping that these wires are similar to what WiFi adapters and actual 3G modems are using). Unfortunately, after finishing the mod and testing the modem, from the usual RSSI of -85dBm (before placing the modem inside the unit) it drops to -90dBm(sometimes -95dBm to -100dBm with SUN network) =( . I'm already anticipating this result. The important is that I can still surf the net (and other online stuffs) without the unexpected disconnection.
I've placed the two antennas in between the touch pad and the right speaker, and put some spaced in between the two. I've also repositioned the modem in such a way that SIM card can easily be accessed by just removing the upgrade panel of this unit.
Finally, the complete internal hsdpa modem mod (somewhat "messy").
Fn+F10 combination is now working (the symbol appears on the bottom right of the screen). The LED indicator, which is shared with WiFi, turns yellow. It turns to blue for WiFi and light-blue when both are enabled. (note: my hsdpa modem is always enabled in my present mod)
Now I have the extra time to revisit this mod. It seems that it's better (in term of signal reception) for the second antenna(?) to be soldered directly to usb modem instead of using coax wire. Below is my latest adjustment. It looks "presentable" now compared to the previous circuit.