922 AIO Printer, White Lines Solution

I have a Dell 922 AIO Printer that is 3 or 4 years old. It's been a very solid performer as a home use inkjet and I would not hesitate to buy another Dell printer based on this one.  

Recently it started to show white lines, or more accurately, horizontal white gaps. Like the snapshot at right. I searched all over but did not find a solution. Available advice generally involves cleaning the nozzles or using the alignment utility. One post suggested to wipe down the clear plastic encoder strip. These things did not help. Being an engineer and a professional problem solver, I decided to figure this out myself. I hope it's of benefit to someone else, as I have often benefited from posts of others.

 First observation is that this is a paper feeding issue, not clogged inkjet nozzles because there is no "missing ink". If you close the gap, the letters would be properly formed. The gap happened about every 37 mm (about 1.4 inches) down the page. I was thinking one of the plastic gears in the paper feed drive system is broken or clogged with dirt, etc. With this I decided to open it up and have a look at the guts of the printer. I realize that a lot of people would rather go out and buy a new printer than do this, but this is for the rest of us. Since it's unusable and there was no other solution available, I had little to lose.  

I disconnected all power and cables, carefully removed the hinged scanner top, being very careful not to damage the 3 or 4 fragile ribbon cables. Then removed the 3 screws in the top cover of the lower (printing) unit. Carefully opened up and removed the snap-in cover using a knife and flat blade. Caution: you may need a second set of very patient hands to avoid damaging the hinges and ribbon cables that connect the scanner top to the base. All the cables can be gently pulled out of their connectors, but it's a bit tricky. Tip: tape the scanner cover to the scanner bed and the scanner support arm to the scanner base so they are not flopping around as you work on this.

Now you are looking into the open case. On the far right side of the main friction feed shaft (the shaft is about 1/2 " diameter and has a rough surface to pull the paper through the printer) is a thin, clear plastic disk. There are very fine black lines around its outer edge which pass through an opening with an optical sensor as the shaft rotates, driven by the motor. This provides an accurate location feedback to the paper feed control.  The disk is hard to reach, so I took a Q-tip with some rubbing alcohol and wiped down both sides as I rotated it via the white plastic gear. Be careful not to damage it. I repeated this until the Q-tip was coming back clean. It looks like a little inkjet mist kind of gets everywhere inside the printer, judging by the other surfaces. So, after a few years of use, it had finally started to make the encoder misread and cause the resulting paper feed problem. I put it back together and it printed beautifully again.

In this printer, and I suspect in many other inkjet printers, there are 2 sets of motor drives, feed mechanisms, and encoders. One for the horizontal travel of the print head and one for the paper feeding. In my searching, I never saw this mentioned. I saw lots and lots of posts asking for solutions to "horizontal' white lines" - many of which did not seem to find solutions.  So, this is my Karmic contribution to those willing to dig around inside the box a bit. Good luck.