Peter,
Most likely: Issues with carts and heads feeding from the left side only (Yellow, Green, Blue) cartridge slots may indicate an issue with the hardware at the left side and/or the carriage head PCB. That mainly checks/controls the cartridges, heads and inkflow. Your new yellow cart must have been a recent date one so should not trigger that warning. It could be as simple as bad contacts at the cart slots and more complex with a bad head carriage PCB.
Thanks, Ernst, for your detailed response.
To recap:
1) Yellow cart and head have both been replaced recently. The recent, re-failure of yellow channel points to an underlying problem not fixed by head and cart replacement.
2) As you say, the new failure of the green channel points to failure of something related to the left hand side hardware.
I did an "all heads" head cleaning, with no change.
Could you both check the firmware version? It may be possible that HP took measures against prolonged use of the chip (either in the firmware or in the cart chips) like we do with our Z3200s, mine Z3200-PS version A.
Yes, mine appears to be the "B" version. Purchased in 2017, I believe.
Firmware is TR12-RB_16.0.1.1
Serial is CN6AS6K011
Product # is Q6721B
HP tech support in Costa Rica says that firmware updating will not solve my issue. He also said that I have the most recent firmware.
He suggests manual cleaning of the head contacts and at least three, from-menu head cleanings of the offending channels.
If that doesn't solve it, replace offending heads.
If that doesn't solve it, "have printer serviced." For me, that's a 1600km return trip to Vancouver. (!)
Are there any diagnostic tools available to test the carriage PCB?
Thanks again for your assistance!