I had yet another very scary experience a few hours ago on my 7900.
Last week...
After a switch to PK last week ,I put the the old PK,MK, and LK carts (which were all at 1%), back in after needing to swap them out with new ones because of a too low to switch error message. This left me with a totally blank PK channel.
After doing a pair clean the PK channel fully recovered and I printed fine.
(According to the notice on cleaning, the printer says you can replace the old carts to continue to use them up afterward.
Today...
With 1% capacity left on my PK, MK, and LK carts,
I started a print job for a client (12 -13" x 19"s on EX Fiber), and did a nozzle check prior to printing, which was 100% good.
To my horror the third print came out of the machine covered with doughnut shaped black spots ( just about this size -o) all over the print, and very faint horizontal banding in the light areas of a foggy landscape scene.
I had the fine banding once before last year, but after adjusting all the recommended settings adjustments in the users guide, I discovered that replacing the carts that were at 1% with the new carts was the fix, and put all the settings back to default! I had never experienced black doughnuts like today though,and deduced that they were nozzle spits possibly due to air that had been introduced in the black channels due to the switching back and forth of the low carts with the new ones. Or pressurization problems in the old, nearly empty carts.
I did get a good nozzle check though!?
My intuitive nature told me to put the new PK,MK and LK carts back in, forget the 1% carts, and do a regular full cleaning thinking the print head must be a mess. It must have been since I got a cleaning failure message on the first attempt, but I repeated a regular full cleaning which worked.
I am now fully convinced that what I experienced was due to either lack of pressurization in the old carts from removing and reinstalling them thus weakening the seals, or when the carts get to a very low point before an " empty -replace" message flashes, the remainder of the ink gets mixed with any air in the cart (kind of like sucking up air at the bottom of an empty drink with a straw), which then goes down the tubes and spits through the head. I believe the dampers are supposed to control that but...
Lesson learned...
I will not worry about a few ML of ink and try to squeeze out the carts when a cleaning requires a cart swap at 1% left!
A few $ worth of ink is not worth the time and materials wasted
As I said in another thread these costs need to be factored in when charging for your printing, even if you are printing for yourself and selling your prints.