For HP 950 / HP 951 / HP 933 / HP 932 cartridges:
After refilling these cartridges, the printer may not recognize them, or may send you an error signal "out of ink". To overcome the chip issue, you can either replace the chip with a new one or follow this procedure:
Use 2 OEM cartridges. You can't refill one & put it right back in --- you have to use a different one, but you can swap them out each time. The printer knows if the previous cartridge was put back into it, but it can only remember the last one, so if you use cartridge #1 & it goes empty, put cartridge #2 in, then when #2 empties, you put #1 (refilled) back in and it should work, and then refill & use #2 when the refilled #1 goes empty.