This concerns the Canon MG6350.Blank page issue, as you describe with your mg7520.
What I state here is true and includes my opinion/free speech thoughts.
I have two of these machines, a white one and a black one. I needed a printer - found the black one in a charity shop. Bought for 10Euros. When home I tried it out and it worked perfectly, cool prints and the way the tray opens auto when printing. A little story here... I have white laptop and white phone and thought wouldn't it be great to have a white printer. The day after I got the black MG6350 and had that thought, I happened to be in a different charity shop and there was a white printer, just arrived. It was exactly the same model but white. I bought it for 8 Euros. Got home and worked perfectly. Very pleased with myself and my luck, I bought 30 generic, ink tanks, cheap ones from the internet. (later on I was to find a big bag of them in yet another charity shop, for 5Euros. Anyway, all went well, I used one printer at a time and swopped them over every six to 12 months so they wouldn't dry out/fail. After three/four years, I had my first problem. The black one stopped printing - or rather it started printing only blank pages, using ink, and same sounds as if printing for real, even with copy or print nozzle pattern, blank, thru wifi and thru USB, Windows or Mac, blank. I did everything I could think of - deep clean, hard reset, reseated printhead, printed from different laptops win10 and macbook, all many times. I had previously (years ago) updated the firmware in both of them (2.050). Nothing solved the problem. Thanks to all who shared their repair success stories for me to try to fix mine.
Anyway, it was really strange the way it printed perfectly one day and next just blank pages. One thing happened just minutes before the blank pages - the paper tray took up about six sheets and came back with an error that the wrong paper was being used for the machine. A friend had also, just before the problem, printed from a Macbook with setting that tried to print from the upper tray (usually disks or photo or envelopes) - this reported 'no paper' as was the case - friend should have used the A4, normal lower tray. One last thing was that it was in the morning. So logic told me ink tanks could have drained overnight due to mis-seating themselves - unlikely. Six sheets of paper could have dislodged the paper feed mechanism somehow or dislodged the printhead going passed (too thick a wad of paper thru the small gap) so one or two pins dis-connected. Macbook could have sent strange codes - the Bonjour network protocol. Waste ink could have been full too, but unreported.
I've read about machines fixing themselves when you put in official inks. Didn't try that as I didn't have any and wasn't going to spend the money. I have had problems with other machines, all using cheap inks, where I am convinced the machine deliberately fakes a clogged/bad inks print output, forces lots of cleaning for no reason, fake error messages, etc..
So what I did, as many of you will have guessed by now, is swopped the printheads. I am pretty sure they were original printheads from new, in the machines, anyway, also pretty sure that they were Canon originals. So did it work?
WTF! IT DID.
Swopped printheads and both machines worked perfectly!
Now either 1 - there is software/firmware code, written by the manufacturer, deliberately, in the printer logic boards that detects generic inks (perhaps printheads too) and cause such problems as force the users to go back to Canon inks/printheads. It deliberately causes bad/broken prints, no prints, ink tank errors, all sorts of errors - in short, it wastes the ink/paper/time so the owner goes back to or tries original expensive ink tanks - that's if they don't decide to get rid of the machine. New original inks or printheads fix the error instantly.
or 2 - the machines suffer code corruption that causes all the above and new original inks or printheads fix the error instantly.
There are other issues where the printer manufacturer can build in a mode or date of death -
For example the waste ink full will be calculated on ink used for setup/cleaning and as soon as you hit a certain number of prints/used cartridges it displays a fault and won't work. Many have found the reset waste ink monitor function and got more life from their printer.
Reading all the trials and errors tried on this and other forums and what fixed some of them, I'm convinced that the home printer industry is secretly punishing/cheating people for using cheap ink. Think of the thousands of machines that have been dumped because of this, think of the frustration, the ink, paper, time and money wasted - this is a terrible thing. This is morally, ecologically, financially and underhandedly WRONG.
