The only sure way I know of to get single carts to print single swaths is through a nozzle check. "Inputting" RGB color levels has to pass through the driver, which then can mix inks in a proprietary way.
If you cant test it, either take a risk and buy it (negotiating the price), or don't. It's like buying a used car without being permitted to take a test drive.
Did you recently change ANY carts?
I'd also suspect the ink, not just the printhead.
It would be great to force a Service Test Print from a Canon Pro-100 (where every nozzle can be individually examined through the "grids". Anyone ever been able to do that?
Since we have had a recent report of a purge system issue with an Epson printer, you might try flooding the purge pads (the station where the printhead parks) with Original Windex to see if you can establish a standing "puddle" on the pads, put the printer through a cleaning cycle, and see if...
First time I've heard of an Epson Purge Unit failure...sounds quite similar to some Canon failures (typically loose or clogged tubes).
As I said, it WAS air (lack of ink in the nozzle chamber). I did not expect a purge system issue with an Epson. Now I know...
A nozzle check print on a PRO-100 (and most Canon consumer printers), prints light blocks of pastel colors, that "should" look completely featureless if good. No streaking or banding should be visible at all.
A service test print (easily to print on older Canons) would show EACH NOZZLE'S...
If you have traces if the PBK segments showing, your print head is working. The ink channels in the head are probably clogged with PBK ink that has solidified. A careful external cleaning program may unclog it.
Another possibilty is the purge system for PBK is also clogged, IF there is a...
I cannot elucidate on a "fatal" error..except for a "failure to power up" (and a new print head did NOT resolve it, (Canon i9900).
I think it's "casual", not indicated with any error "readout", but others can chime in.
The most common "fatal error" is the frequent situation where a failure causes the printer to not even power up! It is common for some diagnostics on the main board to to prevent an "All-OK" signal being sent to the power supply to fully power up (without removing the print head or some other...