How do I clean the printheads of an HP Designjet 500 42-Inch Roll Poster Printer, HP's P/N: C7770B

[JohnL195]

Could you please tell me or give me instructions on how to clean the printheads on the HP Designjet 42-Inch Roll Printer, HP's P/N for that Poster Printer is: C7770B

When I am printing a picture or a poster with the HP DesignJet 500 42-Inch Roll Poster Printer, it fills the paper with blue and gray ink and it does not print/show/display the picture that I printed using that printer. 

[jasonmiamifl]

easy.. when power on & carriage box start to move to left, unplug it.

move carriage box to left & open the cover. Myself use a paper towel & rubbing alcohol. also clean contacts.

Clean the encorder strip, the silver metal rod & lubricate as well...

[davidzuts]

You probably need to replace the yellow and magenta printheads.  Cleaning never brings these heads back. You could try to put them in hot water (tea temp) for about 2 minutes each and then blot on a damp paper towel as you should get 2 full lines of color. If you do not then the printhead needs to be replaced plain and simple.

[JohnL195]

Could you please attach a picture of the carrige box and what encoder strip and silver metal rod are you referring to?

Thanks