[palito]

I have an hp 5550 that prints half an image then the yellow stops printing. If there are two images on the page it will print the first half then the yellow stops printing, then next image is ok until yellow stops in the middle again.
Yellow bars down the page print ok and so does the utility test prints. Image files print normally at a bureau.
The yellow doesn't stop at exactly the same place every time, but close.
???

[tooki]

When the yellow stops, does it stop cleanly, or does it kinda fizzle out or fade?

I assume this is an inkjet. If that is the case, my inclination is that the cartridge is defective. I'm not too familiar with HP's cartridges, but when you first open them, is there a piece of plastic film you have to peel off, as you do on most Canon and Epson cartridges? If so, check to make sure it got peeled completely, because what you describe is symptomatic of a cartridge that's having trouble letting air in to replace the ink that's being used.