USB-C to HDMI adapter no longer detects an external monitor.

[Adam20m]

The adaptor "HP USB-C to HDMI 2.0" I have been using with my laptop suddenly stopped recognising external monitors. The adaptor and monitor work as I checked with another laptop. Also, my laptop (HP Spectre x360 2-in-1 Laptop 14-ef2015na) works with any other docking station connected to USB 3 or Thunderbolt port.

It only stopped working with the USB-C to HDMI adaptor. Actually, tried 2 different adaptors (one is HP) a none of them work now. Both were working previously for almost a year with no issues. There is a usual sound from the laptop confirming a device was plugged in, but the monitor is not detected. Any ideas what the problem could be?

[Adam20m · Accepted solution]

For the benefit of anyone who may face a similar problem, the fix in this case was very simple. All I had to do was to perform a hard reset to cause a capacitor to discharge. This is done by holding the power button for 20s and then starting the laptop again. After that all adaptors work perfectly. I guess, the capacitor was maintaining voltage on the Thunderbolt ports, and a normal restart was not sufficient. This is credit to the HP advice I got on WhatsApp. Thank you HP for very fast and correct diagnosis.