New Pavilion laptop - spec says that USB-C connection supports Displayport 1.2 alternate mode.
Want to connect 4K monitor via Displayport to get 60hz refresh rate - connection via hdmi cable works but is only 29hz.
Have tried 3 different cables all spec'ed to support this but none work. Still have two cables which are being used to test. Monitor works correctly over Displayport with either of these cables when connected to another laptop (Dell).
The cables don't work with the laptop 'as shipped' or with intermediate stacks as bios/firmware/software updates installed per the HP Support utility.
The retailer technical support team went through their standard diagnostics (including a clean reinstall of the system) and agreed that there was a fault versus the claimed specification , they exchanged the laptop but the replacement still fails.
Have tried uninstalling all the USB hubs (the hidden one's as well), disabling any power saving on the USB (and graphics).
In all cases the external monitor has no signal on the displayport connection and the laptop doesn't detect the attached monitor.
When either cable is plugged in, the 'USB connected' beep occurs and a warning message flashes up saying the USB connection may be limited (this doesn't happen when connected to the Dell).
There is a difference in the connected USB devices (in Device Manager)
For one of the cables there is a USB Device - USB 2.0 billboard, for the other it is called DisplayPort Alternate
It looks like the cables are being recognised (at some level) but there is no signal being sent/received along the wire.
Suggestions please