HP 940 Strangeness

[Richard Steinfeld]

I'm noticing a strange phenomenon about my HP 940C printer and color
cartridges, type 78.

My last color cartridge was replaced early because I got a "bad
cartridge" failure.

Today, I got the message on-screen that my color cartridge is low on
ink. Within only a couple of hours, with no printing, the printer now
indicated that the cartridge is bad.

I cleaned the cartridge contacts and printer contacts with alcohol;
cleaned the print head area. I ran a test print (the butterfly), which
printed nicely. I cleaned the cartridge and print carriage contacts with
a good-quality classic electronic contact cleaner/preserver that's
leaves a very light oil film.

The printer is still running the carriage over to the "bad color
cartridge" indicator. But the lights don't indicate any problem. No
messages are coming from the software.

The next thing for me to try, I guess, would be to place these two
cartridges into another HP printer that takes the #78 and see if these
printers give the same indication. I haven't done this yet.

What is going on?

Richard

 

[Bob Headrick]

I'm noticing a strange phenomenon about my HP 940C printer and color
cartridges, type 78.

My last color cartridge was replaced early because I got a "bad cartridge"
failure.

Today, I got the message on-screen that my color cartridge is low on ink.
Within only a couple of hours, with no printing, the printer now indicated
that the cartridge is bad.

Try the diagnostic test as follows: turn on the printer. Press and hold
the power button, then press the X button 8 times, then press the formfeed
button 4 times, then release the power button. This will print a nozzle
diagnostic page. These nozzle patterns should be ramps with a roughly
rectangular shape. If a large block of color is missing, or if regular
repeating patterns are missing from each color it indicates an electrical
issue. Since you have scrubbed the contacts it is probably not an
interconnect issue. It *is* possible the cartridge has failed. If the
nozzle pattern is OK and the printer will print I would ignore the error
position.

Regards,
Bob Headrick, MS MVP Printing/Imaging

 

[Arthur Entlich]

I agree that the next step is to try the same cartridges in another
printer. That might help to determine if the problem is the cartridges
or the printer circuitry.

It might be a bad sensor. All to often, sensors to detect failures of
other components fail themselves.

Art

 

[Richard Steinfeld]

I tried this cartridge in a different printer. It passed the simple
self-test. I'll try your diagnistic now.

Thanks, Bob!

Richard

 

[Richard Steinfeld]

Nozzle pattern came out as follows:
Magenta: a few dropped lines.
Cyan: more dropped lines
Yellow: I could only see the first strong bar; couldn't see any further
lines.

With the earlier cartridge for which I received a failure notice, only
the magenta was present (I didn't try the pattern test with this one).

What I'm assuming is that I just go through more yellow and cyan ink
than red. Is this a reasonable assumption?

Thanks again.

Richard

 

[Richard Steinfeld]

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

 

[Bob Headrick]

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?

[My first reply seems to have been lost in the ether....] You are mostly
correct. Single nozzles shorted or open do not cause the cartridge to be
rejected. Typically before each print job and at power on the printer does
a check of the cartridges and will "complain" if too many are open or
shorted. How many is too many will vary depending on the model and what the
past history of warranty calls had been. (A too aggressive algorithm
results in more calls for cartridge issues but less damaged printers. A too
lax policy results in less cartridge calls but more printer damage.) My
recollection is that about 20-30% of the nozzles can be reported bad before
the printer will refuse to print but it has been a long time since I worked
on the 78 cartridge.

Regards,
Bob Headrick, MS MVP Printing/Imaging