HP officejet 9120 inserts blank space

[Printi]

Hi,
Can anyone tell me what the problem might be. I gues it's hardware related since it appears in the demo page printout also. The printer inserts blank space in the printout, about 3 horizontal blank space lines about a half inch per page, random placed. The printer has only printed 3000 pages total.

[Mark.]

just to state the obvious....

have you put the printer through all its cleaning/maintenance tasks?
like nozzle cleaning, printhead alignment etc.
when's the last time you checked/cleaned/replaced the rollers or drum or toners?

[Geek-9pm]

That printer can  do 50,000 pages before major repair is done. Or is should.
Cleansing and replacing ink is normal. A major repair is when you have to hire somebody to take it apart.
Amazon no longer has that printer and it got bad reviews on Amazon.
You can buy a similar printer for under $100 plus shipping. 

[Printi]

Yeah I know it's old and big, but for me it's a keeper. Because I have lots of large ink tanks and spare printheads and I also have the A3 hp business inkjet 2800 which uses the same inks. It's not allways that bad an idea to have something no one else want to have        
The print quality is fine and the printheads also. Nothing misses in the printout, the printer just add blank horizontal space.  I don't know how the paper handling works but perhaps there's a sensor or something else that needs to be cleaned.

[Geek-9pm]

Are you sure it is not an issue with the print heads?
Anyway, here is a simple test sheet of vertical  color lines.

Does it print it alright? 


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[Printi]

Transformed into windows

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[Geek-9pm]

That does not look good at all. I have never seen that on any printer ever had of the past twenty years or more. Most lively you already tries another print head and the did not help; - Right?
Here is some stuff from HP:
https://support.hp.com/us-en/document/c00068745
Which leads to:
https://support.hp.com/us-en/product/hp-officejet-9100-all-in-one-printer-series/376170/model/376175/troubleshooting

Maybe you need the roller kit. I do not have any knowledge about this.
The kit is sold by HP and vendors like Amazon.
Picture below:

Amazon lists used kits for almost $200. But for that price you buy a printer that performs most of the same functions.

As I said, I have no knowledge of this. Found it in a Google search. 

[Printi]

Sure I'm not going to pay 200$ for a spare part, but I might be lucky to find another used printer for the price of almost nothing.  For me it's more interesting to use hardware that other people just throw away. Thanks for the effort trying figuring it out.

[Geek-9pm]

Your are welcome.
I am very sure that the roller is the problem. But I can not prove it and I do not have actual experience with that part. I understand what it does and I understand that one kind of failure is to insert repeating large blank areas in the printout. It is very hard to find an reference that explains that in so many words.
Sorry I do not have any references.