dropouts are not clogs. they are a lack of ink to the nozzles!
fault...
low pressure to carts - bad cart seal - cart levels very low- ink draw back due to too many cleaning cycles in succession
it only takes one bad seal in one cart to de-pressurize the system and likely a pair dropout or cart with very low ink will be the first to suffer. Happens some times after a PK to MK switch.
fix...
do not freak out and do power cleans or even regular cleans in succession,it will only make things go downhill fast!!!
Turn printer off, wait a short time (or overnight ) let the printer rest, turn printer on which re-pressurizes the system and carts
print a nozzle check only, if still having same dropout, repeat on off to re-pressurize again. If a cart or carts are at 1% put new carts in and forget the old one (not worth a few $ in ink to blow a head) and repeat the on off and nozzle check only cycle -do not print yet until you get a good nozzle check.
printing more without ink will surely damage the head!!!
BTW the printer does not differentiate a clog from a dropout when it indicates "needs cleaning" a couple of gaps in a test pattern is a clog anything more is usually a dropout due to lack of ink in the nozzle color channel. These printers will automatically initiate correct action to remedy a so called "clog" as long as allowing auto "cleaning" is not switched off. They are very self aware with the sensors that are built in to the system!
I agree with much of your analysis. As a matter of fact I follow much the same routine myself, although I have the "auto clean" turned off with the 9900. The part I find confusing is your definition of a clog as opposed to a dropout. Indeed, the cause of a dropout is no ink getting to the nozzle or past the nozzle. There's a very fine distinction there, since a clog can also be the reason that no ink is getting to or past the nozzle. I suppose it's really a matter of semantics. A couple of days ago I was running a fairly large quantity of prints and it suddenly became apparent that I had completely lost the Y nozzle. When I say "suddenly" I mean the previous print was fine, no problem. I can rationalize calling that a dropout(your definition), since it happened so suddenly. I did a regular pairs cleaning and then ran a full colour print to activate all of the nozzles. No pattern in the nozzle check. Wait a few minutes and then another regular pairs clean and a print. The next nozzle check showed signs of life, but mostly blank space. Again, I waited, ran a print, power clean and nozzle check. At that point I had a full nozzle pattern and it has be good since. If this sort of thing happens late in the day I will usually shut sown the printer and leave it overnight. The next morning seldom shows any difference, but it seems to need less work(cleaning cycles etc) to bring it back to life.
I suppose my only issue with what you have written is your statement that "dropouts are not clogs. they are a lack of ink to the nozzles!". However, my opinion is that the lack of ink to the nozzles can definitely be caused by clogs(sort of a chicken and egg scenario). Also, as an aside, I have found that printing with a few gaps often has absolutely no negative effect on the finished product. Without a densitometric measurement one would never see a difference in most cases, so it isn't always necessary to run cleaning cycles simply due to a couple of nozzle gaps. Give it a try and if you do see a problem attack that, but I think you will notice that it may not be an issue. Of course one would want to keep an eye on the situation and not let the gap(s) become any larger, since they will certainly cause a problem at some point.
Gary