"Jeff Liebermann" wrote in message
...
On Tue, 15 Jul 2014 11:53:22 +0100, "Arfa Daily"
wrote:

I'm assuming that the 'chip' on each cartridge is a simple dedicated
microcontroller, so some level of Vcc would be required to run that, and
it
would make sense to design the chip to run off a rail that would provide
suitable levels for the bus signals as well

Yep. That's what I just found. HP C7250 AIO printer.

There are 4 pins on each cart. I'll arbitrarily number them 1-4 from
top to bottom.
1 +3.3v DC
2 Data cartridge -- printer
3 Data cartridge -- printer
4 Ground

OK. Did a quick measure on the bad cartridge, and it goes 1.2 ohms 3 to 4,
so that ties in nicely with what you found with your checks, and the
symptoms that it caused my printer :-)

Arfa