So, I just got a secondhand PIXMA MG7520 from facebook, it was 20 bucks and working (the only images was it off and it on with the inktray up, ironic), so I get it home, hook it up and it shows the fable “printerhead invalid” and in my case I couldnt even get to the menu so literally stuck on the error, I tried resetting it, I washed the head off, cleaned the contacts with alcohol, cleaned the contact surface inside the printer, tried resetting the cartridges and nothing. after punching it a few times I decided to take it apart because since it doesn’t “work” I cant make it worse, I took the leftside panel off and saw the three ribbon cables going to the head connector and I just started unhooking them, and turning it on to see what happened, until I got left with the combination of leaving the center ribbon cable off and the two corner ones on and to my surpise.. it finally got to the **bleep** home screen, I tested scanning something and printing it, it worked, tested printing a calibration page, it worked, connected it to my wifi and sent a test page from the computer.. it also worked. So I have no clue what that middle ribbon cable does but for some reason it worked for me, and as soon as I plug it back in, it throws the error. (its also reading toner levels) So I’m not saying “do this!” and I dont know the longterm effects, but it worked for me, if you have nothing to lose.. maybe give it a go. In the future I might take it apart all the way to the head assembly and see why that particular cable is wonky.
