Got a USB-C port that appears to be broken? Perhaps your GoPro or a copter has a USB-C port that you think might expose debug connections? Maybe it's just a mysterious port on your laptop that has no markings and you're trying to decypher its purpose? Here's a low-level USB-C debugging and testing probe! This probe can help you figure out what the USB-C port supports at a glance, find any hidden features, and see if anything's broken, whether it's the connector or the USB-C electronics.

With this probe, you can:

• test for a mechanically broken USB-C socket (in laptops/phones/etc) and see which pins have intermittent connections
• check soldering of a USB-C socket after repair
• see if any of the pins are shorted out (soldering issues, broken PD controller etc)
• see if the USB-C port might support USB3/DisplayPort/Thunderbolt
• find hidden debug signals on SBU or any other pins
• see if the USB-C port is a passive (resistors) or active (port controller IC) one
• learn more about how USB-C ports in your devices work!

This probe uses a tried-and-true method of testing electronics - you can already buy RAM, CPU and other testers that work in this way. Specifically, it passes a small amount of current into every USB-C signal pad through an LED and a current-limiting resistor, with current applied in reverse so that it goes through the internal ESD diodes of any active circuitry connected to the port.

You don't need this probe for simply using USB-C in your day-to-day life - the USB-C standard makes it safe to connect all sorts of devices together, at worst, they won't work, but they won't break either! However, if you're having USB-C problems or if you're tinkering with USB-C in your day-to-day life, this probe can give you some much-needed insights into what could be going wrong.

How To Use

Just plug the battery into the probe and plug the probe into a USB-C port you want to test! If there's nothing connected to a specific USB-C port pad, the corresponding LED won't shine, if the pin is short-circuited to ground, the LED will shine strongly, if there's some circuitry connected to the port, the LED is going to shine normally, and if there's only a resistor connected to a pin, the LED will shine weakly. If you want to measure any specific signal to learn more, you can unplug the battery and probe the signals with a multimeter using this board as a breakout, too!

You will need a CR2032 or CR2025 battery - I can't include one because shipping batteries is tricky, and it's easy to find a spare coin cell wherever you are! You can safely leave the coin cell plugged into this probe - it does not discharge the battery as long as the LEDs are not lit.

What To Expect

Here's what you can expect from different kinds of USB-C ports, some broken and some working. It's best to power off the device you're testing if you want to get proper results - that said, you will get results nevertheless!

Here's my laptop with fully-featured Thunderbolt ports - all CC/SBU/USB2 pins light up, and only the high-speed data ones stay off - those pins have series capacitors attached, so they light up momentarily when I plug the tester in but then they stay off.

Here's the USB-C port of a Raspberry Pi 4. You can see that the USB2 data pin LEDs are shining normally, and the CC pin LEDs don't shine as brightly - this is because only 5.1K pulldowns are connected to the CC pins and there's no active circuitry; this is a simple sink-only port with no digital PD.

On a USB-C dock of mine, only CC pins light up. Indeed, when I disassemble the dock, it appears it has a 6-pin USB-C socket, which only exposes VBUS, GND and two CC pins - this USB-C port is only for an external charger and is not data-capable, so I can't plug a flashdrive into that USB-C socket and have it work.

Here's a broken laptop I have, where the USB-C ports are damaged - I'll have to replace this laptop's PD controllers to make the ports work again. Some CC pins are shorted to ground and the LED shines stronger than on other pins, which is consistent with the USB-C port working in only one orientation out of the two.

On a motherboard I got from a cheap laptop, only CC, data and high-speed pins light up - SBU pins stay off. This is consistent with a laptop that only supports USB3 output on its port, and might not support charging - which is how low-end laptop USB-C ports tend to work. That said, if you want to test charging, it's enough that you plug in a USB-C charger and see if it works, it's safe to do so with USB-C - if there's no charging support, the laptop simply won't charge and that's it.

This is a fully open-source product! Use the "Design files" link below to get the KiCad files for your own research.