I've learned recently that a dirty encoder strip can cause a Roland to do all kinds of crazy things that you might normally think are related to head problems or ink flow problems. Dust and dirt can make electronics go haywire.
You first have to remove a few pieces to get the cover off. You'll see the encoder strip standing vertically along a channel that the carriage runs up and down. Push the carriage to one end. Clean as much of the strip as you can. Be gentle and only wipe in one directly. I was told to use a lint free cloth. I used sponge cleaning swabs... a lot of them. But I was a nervous wreck and wanted to make sure it was clean and didn't want to damage anything. DO NOT USE ANYTHING STRONGER THAN 70% ISOPROPYL ALCOHOL or you will risk burning the strip. Don't use head cleaning fluid or anything else. When you have the strip clean, push the carriage back to the other end and clean the other end of the strip.
I was kind of surprised at how much overspray, dust and nasty balls of ink covered dust were all over the inside of the printer. I guess it's been 4 years and we had never taken it apart, so I took a small electronics vacuum and cleaned out the area where the main board is.
Cleaning the encoder strip solved all the crazy problems we were having with random 1" bands running partially through prints. It's an easy and FREE thing to try if you're having random problems.