Experienced help with iPhone water damage. I cant figure this out.

Ok so I own an iPhone repair shop and have repaired hundreds of iPhones.

This is the first time I have ever been completely stumped.

so there is a water damaged iphone.

I did the typical troubleshooting taking the phone completely apart (which honestly didn't look bad at all on the inside, in fact it was still wet when I got it)

I cleaned EVERYTHING even under the plates like usual put it back together and nothing.

so naturally I took my battery from my working iphone 4. still nothing.

finally I thought maybe its the screen ..since i didnt want to waste time with variable i took my screen off my iphone 4 and tried it since I knew it worked with my battery. nothing.

then I decided maybe it was the motherboard. took the water damaged motherboard and put it in my iphone. the water dmaged iphones motherboard worked perfectly.

then I decided maybe its the dock connector power so I took the water damaged one out and tried it in my phone and it worked fine.

I am completely stumped.

what could possibly be wrong if I know for certain that the screen,lcd, motherboard, battery, and dock connector are all working perfectly?

ugh someone help this is driving me crazy!