Hi can anyone help. Changed cartridges on HP310 . Now have problem as some colours coming out magenta. Had somebody out to repair - cost a fortune, but unable to find the problem. Could this be a problem with faulty cartridges, EVerything else checked out by service and nothing found. Don't want to have to pay for somebody else to come out and say the same thing. Do you have to change all the cartridges even when some are not empty. Do the cartridges all have to be same brand or code number. Any help much appreciated