For a long time, my primary printer has been an HP Photosmart series
all-in-one. It's a 6 ink job, which makes it expensive to replace inks if
you use the genuine HP article. So, for several years, I have been using
cheapo eBay inks. They come from China originally, and the most recent ones
I have been using, have translucent cases so you can even see how much ink
is actually in them. They are high capacity cartridges, and the chip on them
says so correctly. I have never had a problem with the printer failing to
recognise them as a high capacity cartridge of the correct colour, and the
usage indicator seems to remain accurate.

So, a couple of weeks ago, I come down in the morning, and it's sitting
there saying "copy abandoned", and the exclamation mark LED is flashing.
Sure enough, one of the missus's documents is in the top that she's
obviously been trying to copy before going to work. So I try the cancel
button - nothing. Nor the on / off button. No buttons work, so I pop the
power, just expecting to get the usual lashing for not turning it off
properly. But no. As soon as it gets going, it tells me that "The following
ink cartridges appear to be missing... " That would be all six of them,
then ...

Nothing would recover it from this. I had a trawl around on the net, and
there was a number of mentions of a couple of caps that bulge on the main
board, so I dived in to check, and yes ! there was one of them. I checked
its ESR for sport, and it was out the window. I stuck a new one in,
expecting all to be well, but it was just the same :-(

A friend lent me a printer in the meantime, while I had a think about this
one. Another friend is a pro photographer, and he has one of these HPs also,
and I knew that he only used genuine inks, so I rang him and asked if he
happened to have any empties laying about. He did, as he takes them back to
Staples, who give you half off in exchange. He came over today with a bag of
them, so I started by taking all of my cartridges out. As expected, it told
me that all of the cartridges were missing, so I put in an empty colour one
and restarted it. This time, it told me that only five were missing, and the
one that I had just put in was nearly empty and should be replaced soon.

One by one, I added 'empty' genuine cartridges, and each time, it read the
cartridge ok. I eventually got to a full house, and all was well. So one by
one, I put my cheapo cartridges back in, and all remained ok, until the very
last one, dark magenta, when back came the message that all six cartridges
were missing. I went and got another from my stock and put it in, and all
was still ok.

So I'm guessing that the comms to these cartridges are just a simple 2 wire
bus, and each colour just has its own address to allow the processor to read
them individually. I'm also guessing that the faulty dark magenta cartridge,
must have a short on one of the bus lines so that when the processor issues
the addresses in sequence to read each cartridge at boot up, none of them
are able to reply so the machine assumes that they are not present.

How easy it would have been for the printer to have just got chucked in the
bin, for what was ultimately a simple problem ...

Arfa