[Samsung Galaxy Note 9 Accessories] Advali:
Edit: Upon more testing, it seems that the method by Hakami55 is much better, it has to be around 15 to 20 seconds. Basically after holding the power button on its on state, we really need to wait for the HP logo to popup around the 15-20 second mark and then once everything turns off, release the power button, plug in the phone to automatically power up. I'll try to post a video once I borrow a phone from a friend.

Looks like for the audio to work, it needs to properly sync up during a full boot and not during standby and pressing the power button removes the audio again. Though in some tests (I had around 30 test, this is a lot for me actually), some of the times, the audio does still work after waking up the device as long as you now plug the cable out.

Previous post:

Dude thanks for giving this method! I can confirm that this method does work for audio but mine is a bit different though based on several testing.

On my lapdock I instead need to do the ff:

1. On the lapdock, unplug all cables. Once I'm passed the HP logo and I'm on the screen with the prompt to either insert a cable or use mirroring, I hold down the power button.

2. Upon holding the power button, I immediately count to 9 seconds exactly, counting to up to 10 seconds will restart the device and the HP logo will show up. We don't want that. Need to do some trial and error to get the hang of it.

3. After 9 seconds, release the home button, the device will still be off.

4. Insert the cable to your phone (or have it inserted on the phone in advance) then insert the other end of the cable on the lapdock.

5. The lapdock will automatically turn on without pressing the power button. After the HP logo, I press the capslock to ensure that the keyboard is working/detected? This will light up and turn off afterwards.

6. Now I can do the right click gesture on the sound icon and select "Display" instead of "USB Audio" to have the sound working.

By the way, I have the smart things service enabled as well in case I can't right click and to select the "Display" as the default audio source.

Sound works everytime now but during the first trials, while doing the right click gesture on the sound icon, the only available option for audio source were "My Phone" and "Display". Lapdock audio will work but you don't want that since the trackpad and keyboard will not be detected. The USB Audio selection should be there in order for the trackpad and keyboard to work.

Also as what was initially noted, pressing the power button will disable the audio again. In my case, when I turn on and off the power button, the screen will be stuck on a black screen. I simply need to hard reset the device.

I wanted to post a video on how I made it work but I only have one phone at the moment and everytime I hit record on the Note 9 while playing audio on the lapdock, the camera will hang or stop recording immediately.

Thanks again Hakami55 for the procedure!

Edit: Upon more testing, it seems that the method by Hakami55 is much better, it has to be around 15 to 20 seconds. Basically we really need to wait for the HP logo to popup around the 15-20 second mark and then turn off. Then release the power button, plug in the phone to automatically power up.

Looks like for the audio to work, it needs to properly sync up during a full boot and not during standby.