If I plug in my speakers on my T520 I can listen to music.
If I plug in my speakers on my T520 when it is docked I can listen to music.
But when I plug in my speakers on the docking station series 3 plus when my T520 is docked there is no audio.

Are there special drivers I have to download for the docking station to work? Thanks.

I have the same dock with a Thinkpad T410 (see signature) - I didn't have to install any drivers, etc for the speaker output of the dock to work properly. I just attached the T410 to the dock and plugged in the speaker cable, the internal speakers were silent by default and the audio output went to the external speakers. Note I'm using Ubuntu Linux instead of windows...

Does the 3 Series Dock support USB3.0 ...???

I am not happy with the dock. Sound does not work until now.

And when I press the dock power button to start the system, sometimes the system starts, sometimes the notebook leds blink and nothing happens.

Well, I upgraded from a T410 to a T420 - and now I have no sound when in the dock.

Fortunately, it was a relatively easy fix. Will place the details here in case anyone else searches for it.

Hardware:
Mini dock plus series 3 for mobile workstations with 135 watt power adapter.
Thinkpad T420 4177-cto

When the laptop is in the dock and external speakers are connected to the jack on the dock using Ubuntu 11.10 64 bit, there is no audio output.

Using your favorite text editor, open the file '/etc/modprobe.d/alsa-base.conf' (sans quotes) - note this will require elevated access permissions (e.g., sudo / root) to change.

Add a line to the bottom that reads:



Next, reboot the laptop and your sound should now be working...

To the original poster I guess this means you may very well have a software related problem, sorry I don't have a Windows fix for you...

I can confirm that this worked like a charm on my W520 running Ubuntu 11.10. Thanks!

I reinstalled Windows and everything works fine now.

Great, glad to hear it works on more than just my machine.