Changing ink cartridges

Your Canon MP780 will have the ink levels displayed on the screen.


Also, while printing on the Canon printers you would usually get a window on the screen showing you the level of ink in the printer.

And here is a link on how to replace the ink cartridges on your printer http://support-au.canon.com.au/contents/AU/EN/8000117601.html

http://driverscollection.com/?H=PIXMA%20MP780&By=Canon

Hello!

Please check the "Rplacing an ink tank" part of the manual. Hope it will help you.
https://manualsbrain.com/en/manuals/1796179/?page=45

Have you checked to see if the jet area on the bottom of the ink cartridge has a blackish sludge on them? It might be that the area that the print cartridges are purged/cleaned to one side of the printer (sometimes called a service station, or spitoon) has built up excess ink that has gotten thick and high enough that as the carriage goes over that area the bottom of the cartridge gets polluted with the blackish sludge. It will work slightly into the jets where the ink comes out and cause discoloration, even after you change the color cartridge. Open the unit to look inside with a flashlight for build ups and clean it (if you find some) with disposable things like cotton swabs, coffee stirrers, whatever you have that wont damage anything inside. Another cause could be mixing of the cyan and magenta and yellow somehow inside making a dark color representing black - but replacing the cartridge would cure it immediately.

I have to ask this question of you, just to make sure this is not an issue. Are you using a factory new ink or toner cartridge?
Please consider the following:
If you are using a refilled (the absolute worst possible choice) or third party cartridges (2nd. Worst possible choice) that may well be your problem. Most manufacturers build logic into their products to prevent the use of “Other Equipment Manufactured” cartridges as well as re-filled cartridges.
They do this to prevent problems from contaminated inks or toner causing problems with print quality or damaging the physical printhead or photo conductors.
If you are using factory new ink or toner cartridges, then please call the manufacturer’s Technical Support for assistance with the warranty on the cartridges
Don

Wrong cartridge means you need a new printhead. qy6-0049-000. Around $59.00. Cartridge in this case refers to printhead, not ink cartridges.

Try to reset to factory .
Remove ink cartridges and print head.
Power off machine and unplug for 10-15 minutes.
Restart machine and install head and cartridges.

http://www.tradebit.com/filedetail.php/3901083-canon-pixma-mp780-mp-780-printer-service

Canon MP780 printer service manual

Basically ##343 means the waste ink absorber needs replacing (soaks the spilt ink up under the cartridges).

http://www.tradebit.com/filedetail.php/3901083-canon-pixma-mp780-service-manual

Link to an official Canon service manual. That should tell you how to change it.

It could damage it further by taking it out. Not to mention messing up the timing of it.

Can you remove the ink jet cartidges from where it is parked at?