T520 poor print quality

[Smcclell]

Replaced printhead due to poor quality printing. Updated firmware and drivers. Job will begin to print fine, then experience sticking and knocking of the print carriage resulting in a section of blurred (almost double strike) printing in the middle of the image. It does not appear to have anything to do with file type or software, I believe it is a mechanical issue.

[Valsimot]

Clean encoder strip to see will that help.

https://support.hp.com/us-en/document/c04061127 

[Smcclell]

I have already cleaned the encoder strip 3 times. Doesn't seem to make any difference. Thanks though!

[Valsimot]

Is the issue always on the same part of the print or does it change position ( left-right) ?

[Smcclell]

It changes position. A few times it started within inches of the beginning, others I made it almost 12-18 inches in before the first incident, then it would correct itself, then happen again on and off until there was no recovery and the image was a mess.

[Valsimot]

Could be the trailing cable losing connection.

[Smcclell]

How would I check that? 

[Valsimot]

Only by replacing, there is no other way to be 100% sure.

Is there any strange noise when this problem occurs? Does it happen when you print internal pages from the printer's menu? The carriage shaft is lubricated not dry?

[Smcclell]

It sounds like the carriage is getting stuck at the far right . There is a clicking sound. It doesn't happen when I print the test pages. Lubrication of the shaft is something I could try. Is there a tutorial for this?

[Valsimot]

Use your finger to touch and feel for lubrication of the main shaft, if it feels like it's dry use a piece of cloth few drops of oil and spread the oil from the cloth through the whole length of the shaft, as far as you can with your hand from left to right.