Once my original cartridges ran out on this Canon MP600, I've been using cheaper refills bought online. I've had no problem until now. I replaced the two blacks a couple of days ago and now I can't get the printer to print black. I can fudge it by changing the paper source to photo paper. Then I can print text but it's very slow and I believe what's happening is that the black is being created by mixing all the colors except the PGBK. My problem seems to lie with just the PGBK cartridge. So I tried another new cartridge and still it doesn't work. When I print the nozzle test, there is nothing for PGBK.

I've looked online for suggestions and some advice is to remove the printhead but after searching for an hour, I can't find instructions on how to remove the printhead on this model.

Any suggestions would be appreciated. TIA

anyone?

I would say you have a bad batch of no name cartridges. Try running a print head cleaning session in the printer settings. If no luck I would go buy a new Canon ink and try it out.