"Wobbly" channels - what is the underlying cause?

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?

Please post a nozzle check image. Because VLM and LC are a channel pair, it’s most likely nozzle degradation and not clogs. If the nozzles are gapping in the middle of the nozzle check this is a stronger indication of nozzle degradation but please post.


I’ll post an image when I get home. What causes nozzle degradation? This printer is relatively young, at least in terms of usage.

Here are scans of some of the nozzle prints. I don’t remember precisely which order these were in, although they’re all from the past three or four days.
The current state is:
Don’t worry about the C or PK - they will clean up in one shot. I only care about the VLM and LC channels.

First the good news: Your print head isn’t dying (except for possibly the PK Chanel).

This printer could actually use a PiezoFlush treatment . . . Right now what I see is simply sediment in the dampers that should be gotten rid of by PiezoFlush or preferable new dampers + PiezoFlush + a clean of the wiper blade and under the head.

You most likely also need to do some preemptive maintenance on this bugger by replacing the dampers (selector unit) and cleaning assembly (pump cap station) before flushing. These two things need to be replaced every couple of years on this model to maintain the proper flow and keep the dampers from locking up.

best regards,

I’ll add a note to this. On closer inspection PK and Green look more problematic re: nozzles continuing to drop out across all checks. This printhead needs to be flushed. It’s not good to print with even a single nozzle out.


This printer has seen relatively light use, mostly because it’s been dead most of the time. It says that it’s printed 500 pages, a significant proportion of which - a third? - are nozzle checks. (Thanks to you and Dana for educating me enough to revive it!) I cleaned the capping station last week, and it had far less gunk in it than any of the others (7900, 9900, my friend’s deader-than-a-doornail 4900). I also swabbed out the dampers, although I’ll admit to probably not having done a terrific job on it.

Could I get away with replacing the dampers, and then doing the PF ONLY on the two channels?

What are the chances of the PK actually being near death? (I realize that this is predicting the future.) If I have channels go out on this printer, I’m unlikely to perform heroics to save it. I’d probably flush it and stash it in the basement (fully climate controlled) in case the Piezography 9900 dies. For color printing I’d almost certainly get a new printer, although I’d be pretty burned up to be doing so.

Don’t worry about PK and G for the moment. I haven’t tried clearing them. I am pretty confident that they will clear if I clean them. The VLM and LC have been problematic and I wanted to clear them before attempting to mess with anything else. If I get VLM and LC cleared, I’ll do the PK and G ones.

I see. Then yeah, if your cleaning assembly is able to get all nozzles back, the cleaning assembly is not the problem and the problem lies in dampers/head (one or both but the dampers go first generally). Best way to do this is replace dampers, do a flush if you can, and see that all nozzles print well over a period of some time. If no, store the printer as backup. If yes, put back into ink.

I’ve taken this leap with 4900s too many times but generally it has paid off.


I don’t mind changing the capping station while the hood is open to change the dampers, but what about the idea of flushing only the VLM/LC channels? Rather than the straightforward way of loading a full set of carts with PF, doing an initial fill, then going back to the ink carts and doing another initial fill, could I short-cut it? Ie replace the parts, clean the head. Get TWO carts for PF, load them with PF, do however many power-pair-clean on VLM/LC will “initial fill” just those lines, then go back to ink for those two carts and power-pair-clean them to reload the ink into those lines.