Elite 1698 board

[Adampark]

Hi all, I am having a problem with a 1698 board it powers on fine then disconnects every  10 seconds if it?s plugged in via usb it doesn?t disconnect  I have had a look over the board and can?t seem too find the problem has anyone came across this before ? I have another donor board which is also faulty powers on fine but the b button is always pressed and also both Thumbsticks point down. Hoping too get 1 working out the 2 if anyone can push me in the right direction.

Kind regards

[Adampark]

 Abit of an update On one of the boards I swapped out u4 off a donor board b is no longer pressed the triggers now work too,  both thumbsticks are still stuck bottom right however they do go too the left positon but as soon as you let go back too bottom right on both sticks can?t go up or down either just left
 on both sticks as soon as you let go they both go back bottom right

Any help would be much appreciated. 

[RDC]

What U4 did you replace? The U4 on the top board is just a switch, then U4 on the bottom board is for driving the left side Rumble motors.
 
Sticks stuck down/right would be no ground on the POTs or the lines shorted to voltage, but then they wouldn't move to the left at all. I'd reflow U1 on the bottom board, that thing has been known to cause weird issues.