1st, the Dell AIO 942. It appears you have "clogged inkjets" on the printhead itself. Usually, a good cleaning resolves this. But, if repeated clean cycles don't work, then the electronics or wire harness is bad. I hardly find that the case though, as the prthd. usually is the issue. The ? is, can you afford repeated clean cycles as it dumps ink through. Using the "test pattern" initiate a self-test printout the ptr. offers from whatever buttons depressed to start that, check results.
1st problem: HP DeskjetD2680 hardwired to a Dell D3000 desktop seems to choke on multi-page print jobs. Need to restart to get the job to finish. Also prints strange characters in some print jobs which the "HP Solution?? Center" says is a memory full problem again requiring a restart.
2nd problem: Dell AIO Photo 942 hardwired to a Dell Inspiron 9300 laptop printing horizontal white lines in the back text every few lines whether printing from the PC or copying. I've done all of the troubleshooting steps at least twice, replaced the cartridges, cleaned the cartridges, etc.. Colors prints ok.