Faded color

[Righ]

This is a continuation of a closed thread https://h30434.www3.hp.com/t5/Printer-Ink-Cartridges-Print-Quality/Faded-color/m-p/8185805#M30005 , dealing with an odd quality issue with cyan color on at least the 6900 series of Officejet Pro printers (examples in that thread from the HP 6960 and 6970).

So, the problem:

"My printer won't print extended solid blue blocks of colour correctly, or photos with large amounts of blue."

The odd bit about it is that the printer passes the quality checks and can print cyan or combined colors including cyan without much difficulty. I say "much", because we (myself and the other poster) were getting some odd yellow patterns on the Test Pattern 3, but I've now fixed these. 

What had happened since my last update was that my cyan ink stopped completely. I then cleaned the printer head using this technique for the HP6950 Youtube (I created my own cleaner fluid using 10% aqueous ammonia cleaner and distilled water, and supplied my own syringe and tube). I also pre-cleaned the bottom of the printer head assembly with wetted butter muslin cloth (or any loose weave soft cloth for soft abrasive action). The clean took about three repeats to work.  On my first attempt I got a good flow of blue waste to the catch paper, but the cyan printer head did not unblock. I tried two more times until the print head worked again. Then I had to run a couple of clean printer head cycles from the printer controls until the ink had fully wicked. 

So, the current results are as follows:

Test Pattern 3 has now lost all the yellow streaks (cf. to scan in link above to previous thread). 

The print test sample is 99.9% correct (you can just see a very faint pink line as marked cf. to scan in link above to previous thread).

I can now even print blocks of light blue (eg. table shading).

But, and here's the rub, large blocks of cyan on the printed page are still of very poor quality:

So, bottom line, I have an otherwise perfectly functioning printer that passes all the quality tests and can print dark cyan large font text or cell shading but which can no longer print large blocks of dark colour with cyan. This suggests this might be a flow rate issue for more intense cyan printing. What do I do:

• Do I repeat the print head cleaning?
• Is there another issue that people are aware of?