If you look at the manual that came with the printer, and look at the cleaning section, you should see a diagram with all of the parts people are referring to mentioned. Head soaks are not something Roland wants the end user doing, and honestly, you probably don't even need to do one. Here's what I would do (and have done in the past).
Do a manual cleaning, and get the capping stations really well. Check for any signs of wear, swelling, or deformation of the rubber.
Remove the black cover on the bottom of the right side of the machine (right below the capping stations). This will expose the pumps. You want to disconnect the black tubes (I believe there are two) running from the yellow capping station, and attach a compressed syringe to the end of it. Pull one of the syringes out, leaving the other alone. It's just there to keep air from going in that tube. You'll want to do this until you see some yellow ink come out. It may take a few times, and I would do it one more time after that. After you pull the syringe all the way out, disconnect it from the tube while pinching the tube off with your fingers. Slide it back in and repeat.
After you prime the head like this, do a medium cleaning and another test print. If that doesn't work, let us know and either I or someone else will walk you through a head soak.
