Cartridge Failure Logic -- HP Cartridge #78, etc.

From my experience with this printer and the two cartridges reported
"bad," I'm beginning to think that the cartridge can report to the
printer when an individual firing chamber is fried. In other words,
since the HP process is thermal, each chamber has a heater, and the
heater presents normally presents a resistance in the circuit. I'm
assuming that the printer looks for that resistance when it fires a
nozzle. If there's no resistance (open circuit) or a short circuit, the
printer will report a bad cartridge.

Do I have this right?

The Photosmart 1115 does not report these cartridges as "bad," as far as
I can tell (I don't have this printer installed yet; just running
self-tests). But the 940 does report them.

Richard

"Richard Steinfeld" <rgsteinBUTREMOVETHIS@sonicANDTHISTOO.net> wrote in
message news:13dv3k35ltpiadc@corp.supernews.com...
> From my experience with this printer and the two cartridges reported
> "bad," I'm beginning to think that the cartridge can report to the printer
> when an individual firing chamber is fried. In other words, since the HP
> process is thermal, each chamber has a heater, and the heater presents
> normally presents a resistance in the circuit. I'm assuming that the
> printer looks for that resistance when it fires a nozzle. If there's no
> resistance (open circuit) or a short circuit, the printer will report a
> bad cartridge.
>
> Do I have this right?

Mostly. I think the check does not actually happen during printing, it
happens before the printing starts. The 78 cartridge has its nozzles
electrically arranged in sets of nozzles in an X-Y arrangement. The self
test checks to make sure the cartridge is not too bad. (Single opens or
shorts are OK, but more than about 25% bad will be rejected if I recall
correctly.) A less severe number of shorted/open resistors could result in
the error being reported, but printing is still allowed. On the other
hand, if the nozzle patterns are good it is probably something else. In
addition to the firing resistor checks there are also checks of operating
temperature and a couple other things that could cause the cartridge to be
reported as defective.

Regards,
Bob Headrick, MS MVP Printing/Imaging