I would include one or two extra steps to Palombian's suggestion. The extra step is the following. Using the cleaning solution make sure that you refill the cartridge with the ammonia solution using the dribble method NOT the fast and furious forced storage clip method. During this process, fill via dribbling over the ENTIRE pad to backflush the pad. Remove the contents via the storage clip contraption and repeat, then use the filled cartridge as per Palombian's suggestion. The other part is to also backflush the printhead with a stream of warm water after the soaking in the ammonia solution as per Palombian. My suspicion is that the filter below the mesh screen on the printhead is blocked with large particles of pigment. By backflushing from the nozzle plate so that the water exits the intake screen, we should be able to slowly push these partciles back out. Do NOT force the particles in the normal ink flow direction. This will further embed the large particles trapped in the filter.
Good luck but my guess is that there is some form of mechanical blockage compromising flow.
Good luck but my guess is that there is some form of mechanical blockage compromising flow.