Black screen after battery and screen replaced?

Water damaged I pod touch 4th gen,I've replaced the battery and screen,iTunes recognizes the i touch but screen still will not come on. I've tried shorting the battery(and heard the "peep",like when you connect your i touch to a charging cord) and I can see all the contents of the i touch on iTunes. The screen is good,I tried it on another 4th gen i touch before installing it. I've cleaned the connectors and tried re-connecting several times,tried letting the battery go dead and then re-charging to see the screen(this worked for another i touch screen I replaced). I'm not sure what part to replace on the logic board for water damage. I've also cleaned the logic board thoroughly with isopropyl.