Today I was reminded of a problem I've not seen in a while (I'll tell you why I've not seen it in ages shortly). iPhone Lightning charging cables that only work if you plug them in one way into the iPhone.
Typically, the problem is that the cable will only charge when inserted one way, but I've also seen data transfer being affected.
Weird huh? Why would the charging cable only work one way?
I've read all sorts of wild theories, but the real reason is quite mundane.
It's corrosion on the contacts. Yes, that simple. Here's an example.
Has your iPhone or iPad stopped charging? Check this first!
This corrosion will initially seem permanent, and it will certainly resist being scratched off with a fingernail.
But it will come off. You just need to go about it the right way.
The best low-tech way to remove it is to hit the contacts with a pencil eraser. Add some elbow grease and the contacts will come clean after a few minutes of intense scrubbing.
I don't like to work too hard, so the method I use is a little more hardcore. I use DeoxIT D5 -- my secret weapon when it comes to removing corrosion on circuit boards and components, especially if they have been exposed to the elements -- along with a fiberglass scratch brush.
This method is quicker, and less likely to cause eraser debris-related problems.
So, why have I not seen this problem in years? It's because I use USB-C Lightning cables. It seems that the connectors on these don't corrode in the same way, so this is no longer an issue.