MacBook Air only switching on with i/o flex cable disconnected

Hi guys

We have a MacBook which wasn’t turning on at all. The battery was charging. I delved inside, and found that by disconnecting the i/o flex cable the MacBook will turn on and operate as normal as long as there is charge in the battery. Plugging in the magsafe will then preserve the battery power but not charge it.

I’ve even managed to connect a flash drive to the USB port on the opposite side of the Mac, and have transferred files and done a time machine back up, and I’ve subsequently updated to Catalina. All I know is that I’m going to have to plug the flex cable back in to get it charged and then unplug it to switch it on.

Is there a way of testing the flex cable for any issues? I’m making the assumption that it’s either that or the i/o board that is at fault and not the logic board, but if anyone knows any differently I’d love to know!

Thanks

Christine