HP all-in-one not printing magenta.

[MalcolmY]

I have an 11 month old HP all-in-one PSC which has been working fine. I have changed the cartridges (black and tri-color(CMY)) regularly but recently my prints seemed to be missing the red colour. I bought a new, in date, genuine HP cartridge but I still had the problem. As the printer was still in warranty I returned it to the store who with very little quibble gave me a new one. This was exactly the same, even with yet another brand new genuine cartridge. I cannot believe that 2 brand new color cartridges have exactly the same fault but equally I can't see why 2 different printers should have the same fault. Any ideas?
I should perhaps add two things: I have only ever used genuine HP cartridges in this machine (I thought that was the wise thing to do while the unit was still in its warranty period). I also have another HP printer, different model, different cartridges, that I have had for nearly 10 years and that is going strong - on either genuine, reman or self refilled cartridges.

[TTG]

Maybe take the printer back and see if the problem can be recreated in the shop with one of their own catridges. Are you sure they gave you a new printer?

[MalcolmY]

Yes, I am absolutely sure that they gave me a new printer. I've seen the two side by side in the store - and checked the serial numbers!
They agree that the problem is there with different (new, genuine) cartridges and is present on both printers.
They are as puzzled as I am.

[beso]

Have you reinstalled the driver for the printer. Maybe it isn't telling the hardware to print magenta.

[tamborine]

Take the picture you want to print to the supplier to check.