Why does it only print sharp if I choose "Plain Paper"?

[Kampy]

Hey friends...

A few months ago I posted here re: my Canon Pixma iX6820, which had started printing black ink all wonky / misaligned.

( here's that post: https://www.printerknowledge.com/threads/alignment-issue-or-bad-printhead-canon-pixma-ix6820.15520/ )

The consensus seemed to be a bad printhead, due to years of using cheap 3rd party ink, which made sense, considering I got the B200 error message. So I finally ordered a replacement printhead– a genuine Canon purchased from Jim at www.inkjetprinthead.com

The other day I was getting ready to install the new printhead, but decided to do a bunch of test prints on various papers first, just so I'd have a nice before/after comparison. But while doing that, I noticed the test print on plain paper looked fine, while the ones printed on Canon "Pro Luster" paper, and also the cheap Koala glossy paper (choosing "Glossy Photo Paper" setting) had the problem issue I'd been dealing with.

So instead of swapping out the printhead, I did more test prints, and found that as long as I choose "plain paper" as my media type, even if I'm using Pro Luster or Glossy or whatever kind of paper... the prints were razor sharp! The misalignment / blurry issue with the black ink was GONE. The color balance and exposure was off, as you'd expect when selecting the wrong paper type in the settings. But the black ink seemed to be laying down on the paper just fine. FYI– I was using the same test page of sample text, colors, reg marks, sample photos etc... but saved 2 different ways– as an RGB .jpg (printed from Photoshop) and as a CMYK x-1A .pdf (printed from Acrobat Pro) and the results were consistent.... choosing "plain paper" resulted in sharp prints, while choosing any other paper type resulted in the black ink coming out fuzzy.

SO... do I have a bad printhead or not? Why does the black printhead seem to work just fine as long as "plain paper" is selected? I'm super confused now– it makes no sense! I have yet to try the new printhead because I paid about $125 for it and I'm no longer confident it will fix this weirdness.

Anyone know what's going on? Should I go ahead and open / install the new printhead anyway?

some photos are attached... the closeups were shot through a magnifying loupe, and the only difference between those 2 prints was choosing "plain paper" instead of the correct paper type

 

[pharmacist]

The problem seems to be the photo black position. Choosing plain paper forces the printer driver to use the pigment black position, which seems to be ok.

 

[PeterBJ]

If you examine the nozzle check closely you most likely will notice that the vertical bars on both sides of the "BK" letters are blurred/fuzzy, like in this post. This is caused by thermal damages of the BK nozzles. According to the druckerchannel.de forum this is caused by an ink with wrong cooling properties. The printheads of the PGI-x50/CLI-x51 generation are very sensitive to this failure and to the failure of the PGBK nozzles. In the PGBK grid the vertical lines become double, This is also likely caused by unsuitable ink.

So the printhead is defective. As it has shown the B200 error it should be removed from the printer immediately even if the B200 error has gone away. The B200 error is sometimes intermittent before becoming permanent. If not removed the printhead might damage the logic board and make the printer a total loss. A logic board damaged in this way might damage a new printhead. A defective printhead might also prevent the power supply from starting so you will have to dismantle the printer to remove the printhead.

Edit: The pigment black ink PGBK is only used with plain paper. It is sharper and more water resistant than the dye/photo black ink BK. The PGBK ink is only suitable for plain paper. It is totally unsuitable for photo paper, as it doesn't adhere well to photo paper. That's why PGBK is only used when plain paper is selected. When all other media are selected dye black BK is used instead.