I have a now-fully functioning 4900. However, about every few days, two channels get some dropouts on a nozzle check. In this case, it’s the last two channels on the right, VLM and LC. Usually one or the other of them will cause minor trouble. We’re talking about maybe five or six gaps in the lines, enough to be noticeable on the finished print, but far short of evoking “OMFG this %#@^! is head dying” sort of reactions.
If I clean the pair, usually the problematic channel comes good and is solid. Sometimes it takes cleaning the pair twice, but usually not. Unfortunately, fairly often the other of the pair picks up some dropouts. As with the beginning of the scenario, a pair clean or two will clear the now-problematic channel - but in exchange, the just-cleared channel returns to its loused-up state. Or more precisely, some other spots will pop up, not the same ones as at the beginning. Eventually enough cleaning cycles will result in them both being clear, and then real work resumes for a couple of days.
My thought on this is that it seems like air in the lines, but I carefully re-primed those two cartridges, and surely now after several cycles of this and the resulting dozen or so cleaning operations on these two channels, any air that might have been in the lines should now be gone.
Needless to say, this is extremely annoying, and of course it’s quite wasteful of those two channels. (Thankfully they are on the same pair.)
What’s going on here, and how do I prevent the problem?