Answer to: pf 04 (3630B001AA) print head for canon ipf 750To access the Service mode just press Paper+Info+Power during the power up. From there do a nozzle check (twice as precise as the user mode test, and the internal software does not compensate for the loss of some nozzles). If you find any line missing of a large portion of the color squares not printing you have some hard ink inside the print head. If it prints OK (that was my case), than the print head is OK, just that the new firmware from Canon is telling you have to pay them from time to time. The print head is "recommended" to be changed annually. You can find a way to decript the Canon programming, or just try to find an older firmware on some forum and downgrade (worked for me). From the service menu you can initialize the counter but in the end the error will show again. I haven't used the head resetter, but that might be a good option (and I'm thinking on buying one too). Good luck!