The print engine and the cartridges used in these Dell Printers are made by Lexmark, unfortunately, there is no equivalent Lexmark cartridge which can be substituted for the Dell J740 inkjet cartridges. The only way that these printers can be run economically is to refill the empty Dell ink cartridges. Dell branded ink cartridges cost around £40 each!! The per fill cost for black ink when refilling is around £1 - £1.50 for the colour it is £1 - £2.00  (This pricing is for formulated matching inks - not "Universal" ink which is cheaper and will not perform to the manufacturers specifications - The chambers in colour cartridges never empty equally so for successive refills it is likely that the per fill cost will be less than if an ink cartridge was completely empty, because of the cost differences - owners of these printers should seriously consider refilling. The Lexmark cartridges made for Dell are not made to fail immediately after the ink runs out and can be successfully refilled many times. Refilling before a cartridge is completely empty is a good way of prolonging the life of the cartridge and getting multiple refills. Recognising the point when a cartridge is near empty is vital to avoid damage to nozzles in the printhead. (These points apply to all inkjet printers which use thermal technology in the printhead e.g. Lexmark, HP, Canon, Brother, BT, Sharp, etc etc and not just Dell) Continuing to print with an empty ink cartridge eventually overheats the printhead, dries ink solid in the nozzles and can burn out individual nozzles. A cartridge with dried out ink in nozzles can be recovered but is an added problem which is better avoided by refilling earlier rather than later and amaged nozzles cannot be recovered. 

PREPARATION CARRY OUT THE FILLING OPERATION ON A PROTECTED SURFACE e.g. spread out a newspaper - keep absorbent tissues handy - Ink stains - so wash hands with soap a water. Do not drink or otherwise ingest ink - Keep well away from children and pets.

Be careful and do not damage the electrical connections