PJ-2508UFE: Heads fail after an up/down movement of the carriage

Due to a too tight cabling, resulting in a poor contact, it might happen that after an up/down movement of the carriage the heads will not print.

If this would be the case the 4 lights on the printhead-board, as marked in the picture, will be extinguished. 

During normal operation of the printer these should be lit all 4.

Solution: restore a good connection of the loose cables.