The diodes behind the ports

The symptom that names itself

One socket does everything: powers the board, appears as a port, uploads. The other does nothing at all — no LED, no port, no sign of life — with the same cable that just worked.

Nothing else on this board produces that. A cable fault would affect both sockets; a driver problem leaves the board powered; a dead chip takes both down. One live socket and one completely dead one points at the one part that sits between a socket and the rest of the board, and there is one per socket.

What the part is doing there

Look above each USB-C connector on the front of the board. The small component there is a series diode: current in one direction, nothing in the other.

It is doing one job, and it earns its place the first time somebody connects a supply backwards — from a bench supply, a battery lead, a homemade adapter. The diode blocks it, the board sits dark, and nothing behind it is harmed. That is the good outcome, and it costs a part worth cents.

The other way it dies is current. Push enough through it for long enough and it fails open — permanently non-conducting — and the socket behind it is finished while everything else on the board still works perfectly.

The two repairs

Both are real, and they are not the same repair.

Replace it. The right fix. It is a small two-terminal part and a fine-tipped iron with a little flux will lift and place one in a couple of minutes. The board goes back to exactly what it was, protection included. If you have never done surface-mount rework, this is a good first job — two pads, nothing dense nearby.

Bridge it. A blob of solder across the two pads makes the socket live again this afternoon. It is a perfectly reasonable field repair, and it is honest to say why it is not the same thing: from then on there is nothing between a supply wired backwards and the rest of the board. The next reversed lead does not stop at a cheap part.

So the decision is about the board's life, not the technique. A board on your own desk, powered from one known-good charger: bridge it and carry on. A board that goes into a classroom, a kit, or a project other people will plug things into: replace it, or retire the socket and use the other one.

Before you reach for the iron

Two minutes of checks first, because everything above assumes the diode is actually the failure:

1. The same cable, both sockets. One works, one does nothing at all — that is the pattern. If both are dead, this article is not your answer.
2. A different cable. Two dead cables in a row is rare and not impossible.
3. Look at the connector. A USB-C socket with a bent or pushed-back contact, or with a pin lifted from the pad, fails the same way and is visible under a loupe. Fix the visible thing before the invisible one.

And if the board is new, stop: talk to us before soldering. A diode that failed on its first day is a warranty question, not a repair job.