iPhone 4, 4s, 5 doesn't charge after replacing everything

Hello everyone,

ive got my own repair shop in Belgium.

i now busy for more than one year.

but still i got some problems with the charging connection of some iphones 4, 4S and 5.

I tried everything i can, like replacing the battery, the dock connector, and other parts, but the problem i still have is that the iphone doesn't charge. After doing a hard or soft reset, theirs nothing changed.

the iphone reacts perfectly on the power of the battery and turns on.

could someone tell me what i can try more at least to charge the iphones?

it would help me a lot..

thanks..