3880: problems after black ink valve replacement


I disassembled the printer, cleaned it as shown in the inkjetmall tutorial video and replaced all dampers and the black ink change valve. After that I got the printer working with a power clean cycle. It printed fine in matte mode for some weeks. Today I wanted to change to glossy: after I issued the black ink change command it didn’t print black any more: a manual nozzle check showed totally empty areas either for matte or photo black mode. The cartridges are half full (weighted them and compared to an empty cart).

I disassembled the printer again, cleaned the head again (with Piezo flush) and after 2 cleaning cycles it shows a complete nozzle pattern and prints fine. Now I am in matte mode, but I am afraid to switch over to glossy.

I can see the black ink switch valve working fine when change is happening: the motor is moving the valve to both positions as it should and as shown in the service manual.

Does anybody have advice for me? What can be wrong? Is this a known issue?