This is an issue that can happen on all Epson based printers. I'm going to explain why it happens because I have seen this issue happen so many times on Signs101 that I think it will help people.
The signal that the head uses to fire the nozzles is created by the processor on the main board. The processor sends a 3 - 5 volt signal out which is not enough for the print head to fire. To amplify the signal, they use a transistor based amplifying circuit. A constant current of 42volts runs to the transistors and the low voltage signal from the processor turns the transistors on and off based on what kind of signal it needs to send to the head. This amplifies the signal so that the head can actually fire.
From the main board, through the cables, to the slider board and eventually to the head, at any point if there is a short in the system one of two things happens. Either the short blows a fuse to protect the system or sometimes the short just mixes the signals for each of the channels together which essentially sends the 42volt signal through 100%. This causes either one or all of the colors to fire at the same time which causes the issue you are having.
It's not an easy problem to diagnose because the short could be anywhere. Most of the time it's either the long trailing cables that go from the main board to the slider board. A lot of the time it's the head cables are damaged. Sometimes it is a fired head, slider board or main board. Sometimes is just ink and dust build up around cables connections. Check out all of your cables and make sure they aren't damaged, dirty, or corroded. If they are, that is your best bet to change. Also, air dust your cable terminals and clean with 91% rubbing alcohol, with the machine off and unplugged of course. Don't use anything under 91% as it doesn't dry fast enough.