I’ve come across a used 9900 for sale locally with a strange issue. The vendor claims that in-between two prints, the LK nozzles began firing the wrong way around. In the nozzle check, all the other channels print fine, but the LK channel is printing with the nozzle check slope in the opposite direction to all the others. The vendor suspects a software/firmware issue and speculates a firmware flash may fix it. (The result in printing is weird ghosting of light black ink printing out of registration)
Any ideas as to what’s going on? I’m curious if the issue is likely to be in the head itself, ink selector unit, motherboard, or firmware. If the issue is the head, then the machine could be used for piezography. If the issue is somewhere else, the head could be salvaged to repair another machine.