The 1390 card in my new E1505(same as 6400) has the same problem. It never worked properly since day one. I've been troubleshooting this for the whole week. I tried with 3 different routers and got same results. The routers are all good because other adapters can work with them without any problem. I tried uninstalling and reinstalling driver, tried old version driver, tried increasing power by changing the card's advanced driver setting,  tried updating routers' firmware, tried removing the cover and keyboard to see if the card and antenna are installed securely, tried safe mode with networking, tried everything I can do with no success. Finally I called Dell tech support. They basically went through the same steps I had done and of course no success. The tech support ran out of options but didn't want to admit it's a hardware defect or driver problem. They say they need to think about if there are other things they can do and will call me back next week. I'm not optimistic.

I finally found the problem and fixed it, without help from dell support. It turned out to be the internal antenna. In Windows, go to Device Manager, open properties for the 1390 card, go to Advanced tab, select Antenna Diversity. The default value is Auto. If I change it to Aux, the card can connect to the router very quickly and maintain a stable connection. If I change it to Main or Auto, the card has trouble connecting to the router and if it does connect, the connection is unstable, and also the sensitivity is very poor. It can detect much fewer hotspots than using Aux. This has nothing to do with the position of the router.

To see if it is a problem with the card or with the antenna, I opened the hinge cover and removed the keyboard to expose the card under the keyboard. Both antenna cables were well connected. I disconnected the Main antenna cable (the white one). The Aux antenna cable(the black one) stayed connected. Then set Antenna Diversity to Aux, tested the connection. It worked. I then connected the Aux cable to the Main connector on the card, set Antenna Diversity to Main. It still worked. Then I disconnected the Aux cable, used the Main cable to connect to each of the two connectors on the card, set Antenna Diversity accordingly, and tested the connection in each case. In both cases, the connection was bad. After these tests, it can be verified that the Main antenna, not the card itself,  is probably bad. But I'm not sure why the Main antenna is not working well. The antenna is inside the LCD panel. To troubleshoot the antenna I may have to disassemble the LCD panel assembly. That may void the warranty so I decided not to take the risk, even though I know how to do that. BTW, getting access to the 1390 mini card does not affect warranty, as tech support said.

This is my first time I order a Dell product and will be the last time, given so many troubles I had.

Darned amazing. I'm over at a friend's house troubleshooting her computer. My wireless was working fine. Her's was dismal. I found this answer on the forum and Shazzam!! it worked.

 

Not going to take the card apart to check the antenna, but going to the aux. did it!

 

Many thanks.

 

George