Return to

How to Troubleshoot USB-C PD issues?

People of Level 1, I need your help.

How can I list PD modes or the PDO’s of a device to check compatibility? Has anyone seen edge cases where only specific devices wouldn’t charge off of a source?

I picked up a Phillips 346b1c ultrawide monitor and it’s been a joy except that it won’t charge my Lenovo Yoga 730 13 when docked. If you boot the system with it docked you get a low wattage warning. I’ve pretty much ruled out the cables, I’ve tried the one in the box with the monitor and 2 known good TB3 cables. The monitor is rated for 90W PD and the laptop is rated for 45W so we are good there, I haven’t had issues with other monitors or various TB3 docks. What gets me is that once or twice I’ve gotten the laptop to charge, makes me think it might be a physical issue on the monitor. Everything works fine if I use a chromebook rated for 45W. The best information I can find says that the monitor is capable of up to 20V/4.5A and the most the laptop accepts is 20V/2.25A. My understanding is that PD will negotiate down to something appropriate but PD 2.0 relies on preset PDO’s, voltage and amperage combos available to the source and sink devices. Is there a way to check the PDO’s on a device through software? If you know anything let me know. I have a ticket running with Phillips support and will update if an RMA does or doesn’t resolve the issue.

Tried testing with ubuntu 19.10
I tried cat /sys/class/typec/port1/power_operation_mode to no avail, there are no ports available under /sys/class/typec/

The two devices are expected to communicate and power supply device is expected to send a table of maximum supported amperages for each of the standard voltages.

Google published the opensource firmware and schematics for a USB-c pd charger back in 2014, but electronics companies would choose different components and reimplement the state machines in PD using different uCs and it doesn’t always work right.

There’s a debugging device you can build yourself described here:

It can help you see if it’s Lenovo misbehaving or your monitor, because you’ll be able to see traffic over cc lines and compare it with the spec.

Probably, what you need to fix your setup is some kind of USB-c power injector dongle.