Canon Pixma MP990: How to do Printhead Cleaning and Deep Cleaning Cycles - YouTube
Canon Knowledge Base - Reseating the Print Head - MP640
Amazon.com: Printhead Replacement, QY6-0072 Single Black Printhead with Protective Cover, High Resolution Printheads Compatible for Canon IP4600/IP4700/MP630/MP640 : Office Products
QY6-0072 Print head fits for canon ip4700 mp640 4680 ip4600 | eBay
Canon Knowledge Base - Reseating the Print Head - MP640