Normally when one channel drops like that it's going to be an ink flow issues such as a bad damper, broken manifold, or air getting in the system through a leak. The fact that there are two full channels missing tells me this is electronic though. My best guess is a damaged head board. Most likely a blow transistor. If you feel like troubleshooting to be sure, do a data swap. Take the cables from the A group heads and plug them into the B group heads and vice versa. You're only taking the cable out of the head, not the slider board. This makes the A group data go to the B group heads. If the problem moves to the new colors, it's almost guaranteed to be the head board. If the problem stays in the same colors, its more likely a bad head or ink flow issue.