I have recently purchased a pair of refurbished 339 and 344 cartridges for my HP 6940 Deskjet printer. Initially I could print, now I have an error status and flashing (right hand) red tear drop on the control panel suggesting that one or other cartridge is faulty. Please could you advise me as to which cartridge I need to replace, and recommend a reliable replacement. I am unable to print anything, and cannot clear the error- status!
27 June 2017