Hi Walker, yes I have a second set of carts, I will try your solution. The last owner didn't use the 7900 for more than 6 months so this channels problem is not a surprise. The end of the green channel is without ink, but the start near the cart is full of green ink, same for orange.
You wrote on the piezography pro forum that an "old firmware does not properly equalize pressure between carts (especially when doing init fills)."
Since I'm using piezo inks I kept always in mind " NEVER make a firmware update, NEVER"... My actual firmware seems old HN029AA (10/29/10?) Last one: HN124G5 - June 2016.
Do you think that it could help (a little bit) for this problem too?
Thank again for your help.