Open up the dock...
The 12 pin connecter inside the dock is as follows..
Pin 1 = 30 Shield Connector **********************add earth here from 5v source....(-)
Pin 2 = 28
Pin 3 = 27
Pin 4 = 13
pin 5 = 19
pin 6 = 18
pin 7 = 17
pin 8 = 6
pin 9 = 7 ******************add power here from 5v source....(+)
pin 10 =3
pin 11 =4
pin 12 = 1+2
pin 1 for neg and is the LH pin.
pin 9 which is 4th pin from RH side..
This is all i did only 2 wires added..
check you dock with a test light and confirm the surrounding pins are not shorting where you soldered.
once this part ok then continue..
1.connect dock to tablet BUT make sure Tablet is switched off at this moment...
2.connect 5v power and earth wires to power source you added to dock from 5v usb etc...
3.plug in OTG dongle to dock and Connect Powered Usb Hdd and Turn on Hdd power supply.
4.Noted is Tablet is Still Off at this stage..You will have a Black Screen and when you plugged in the
power for the HDD its now showing the battery charging icon similar to when you plug in a wall charger.
5.Now Turn tablet on but dont press any thing or do anything just let it load up and go to lock screen.
6.In lock screen you now should see "charging"...
7.swipe screen and let Tablet turn on.
8.wait for superuser permissions to load paragon or what ever you are using.
9.open Paragon and check drive is recognised and also mounted automatically ..if not mount it now manually.
10.open up my files and open location of drive to view contents.then open up a movie from the contents of the drive
11.play a movie using the MX player app.
12 Pause it and go settings/aboutdevice/status of battery and see that battery is "AC Charging".
13.your drive is mounted and working and you are now OTG host mopde and charging at same time..
Also if this doesnt work...It might be kernal related..I can confirm it worked on ICS..but havent confirmed JB yet.
hope this helps you...