Printer stopped printing black

I am having a similar problem,Black not printing,HP techinician in Phillipines suggested Head cleaning,but never gave me advice on how to do so,can anyone who had had success pl give me details on How ? Appreciated. Thanks

I have an HP Photosmart 6520 that had the same problem; apparently, it is a common fault with this series. The problem was a clogged print head; the solution: After placing a damp paper towel (solution of 50% water/50% Isopropyl Alcohol 99.9% pure) in the print channel, pushing the print head over it and leaving it to soak for a while, I had some, limited, success. I decided to do a thorough clean to see if that would make any difference: this required taking out the print head. To do this you need to remove the top cover trim to gain access. Lift the cartridge access cover: you will see a retaining strut on the on the rear, right side, edge; it unclips at the top. Heat the clip and lower the lid slightly, then pull on the top of the strut - this is brute force and ignorance time! There are two T10 screws on either edge, two inboard at the lid hinge plate and two under the digital display interface (which pulls forward). After removing all the screws, the trim can be lifted free: there is no need to remove it entirely - place something like a cushion under it and lay it forward. Remove the cartridges and then the springs, placed either side at the rear of the print head: the closed ring on the bottom retainer, the loop on the top of print head - do not reassemble the wrong way around! Slightly lift the print head from the rear; there is a ribbon strip it hooks onto - be careful not to break it! (The ribbon can be detached, but is a pain to reinstall!). You will then see that there are connections on the rear, and very little wiggle room, these are NOT plug in connectors; they are ribbon cables - DO NOT pull on the white "connectors" as the part from the logic board extremely easily and cannot be repaired, rendering the print head U/S. You can now CAREFULLY remove the print head. Start by using the alcohol solution on the paper towel to gently remove excess ink from the print head; you may find there is a build up of crud around the injectors which will require very careful removal with a small flat screwdriver tip, or some such object - be VERY CAREFUL not to damage the surrounding area; attempt this AFTER softening the crud with neat Isopropyl on a paper towel: you can then proceed to flush out the nozzle with neat Isopropyl. This is a VERY messy task, requiring careful spillage control (putting plastic or old rags o your work surface), old clothes or coveralls and latex gloves. Reassembly is the reverse order; taking great care when replacing the print head. Whilst I was about cleaning the Black nozzle, I thought it judicious to clean the coloured at the same time. After I had reassembled mine, I printed a few pages to run ink through the print head finding that, after a few tries, it printed as good as new. Disclaimer I CANNOT guarantee 100% success - but it worked for me!