What I normally do is to try to isolate the issue from several possibilities to one. The only way to do that is to swap dampers. Follow these instructions to see if it is the damper or the print-head.
Perform a nozzle check, and note the bad nozzle check and note one of the white channels that are printing well.
(1) Pinch clip the line closed on the color that printed well and the one that is giving you trouble.
(2) Swap those two dampers. Put the damper for the colo that is printing well, on the print head port of the color that is printing bad, and put the suspected bad damper on the print head port of the color that is printing well.
For example, let's say on my nozzle check I can see that Light Magenta (White) is not printing at all on a nozzle check, but my Light Cyan (White) and my Light Black (White) is printing fine. I would pinch clip those two lines shut so I do not get any liquid on the print head during the swapping process, and then I would remove those two colored dampers from the print head and swap them out. Place the Light Cyan on the Light magenta port, and the Light magenta on the Cyan port.
(4) When the dampers have been swapped, open the pinch clips for those two lines and do 4 head cleanings, and follow this up with another nozzle check.
(5) Note the nozzle check.
The last three colors of your nozzle check represent the white channels, The Lighter Cyan, Lighter Magenta and the lighter Black (Gray) all print in white ink on your machine. In our example before we swapped dampers the Light Magenta was not printing at all or is printing broken up. The first white next to the yellow printed well. The light Cyan which printed well before we swapped dampers shows that Light Cyan's print head channel and damper are not clogged. So when we put that damper on the problematic color (light magenta), Then we will get one or two possibilities. Either the middle will print with the light cyan on it. Or it still will not print. The same hold true for the Light magenta which we put on Light Cyan.
If after you've swapped the dampers and you see that the middle white is printing again, then this would indicate that the Light magentas damper is bad, since there is evidenec that the print head allows the print on the Light Magenta channel. Further evidence of this can be seenw hen looking at the nozzle check Light Cyan print. If the first white (The white next to the yellow) did not print, then this would indicate that the light magenta's damper is bad.
This illustration below portrays a nozzle check with the light magenta not printing as in our example.
If after you swap the dampers and you find that after 4 head cleanings your nozzle check now looks like the image below (The Light Magenta, Light Cyan, and Light Black would all print in White on your print bed), then your issue would be a clogged damper.
Note that the problem followed the damper. We can safely say that the White Ink on the Light magenta channel on the print head is not clogged because the Light Cyan printed on it.
Now if your nozzle check looks like the sample below, then this would indicate that the print head is clogged. Note that there is no change from the original nozzle check after we swapped dampers. The Light Cyan (White next to the yellow) Printed fine with the light magenta damper on it. This proves the damper is good but the Print head channel of light magenta is clogged. See Flushing instructions below to flush the line and print head.
If your Nozzle check looks like the one below, this would indicate that both the damper and the print head are clogged. Note that both colors are not printing well. The light cyan did not print because the Light magenta that we have on that channel is clogged, and the Light Cyan damper that you have on the light magenta channel did not print because the print head was clogged.
Just to be sure, if you do get the above nozzle check, then do 2 more head cleanings, and let the printer relax for about 30 minutes and then and then do another nozzle check to see if it is still the same as above.
Flushing the Print Head
Using approved flushing solution only, flush out the line which has the clog in the print head completely. You'll want to see that the ink tubing is completely devoid of ink and is translucent. After this you need to perform at least 20 to 25 head cleanings. The only way we can get the interior portions of the print head flushed and cleaned is to get the piezo-electric crystals to move in each channel, the only way to get them to move is by way of a head cleaning. The more head cleanigs you do with flushing solution, the more resident ink that may be lodged into the print head can be flushed out. SWF East recommends no less than 20 head cleanings to get the most out of your flushing procedure.
After this is complete, perform another nozzle check with the flushing solution still in the line, we don't want to introduce ink into the line if the clog happened to be beyond clogging, this would be a waste of ink. When you do the nozzle check with cleaning solution, you'll want to watch the nozzle check as it prints, due to the fact the flushing solution tends to dissipate in the open air rapidly. Do a couple of nozzle checks to confirm that the print head is unclogged.Once you have confirmed this, re-introduce your ink into the line followed by 3 head cleanings and perform a nozzle check with the ink in the line.