No HDMI signal from new Manjaro Community Edition phone dock

[wibble]

Could somebody please explain this:
The same monitor using the same HDMI cable but branched to an ordinary X86 PC always worked. So I just wonder what makes the difference??

Different hardware, different driver, different platform and possibly different HDMI version. There's quite a lot of scope for little differences to cause a problem. I'd be more interested in the differences between the monitors that work and the ones that don't - that might help narrow down the possible cause(s). Are the HDMI versions different? Does it only happen with certain resolutions, refresh rates etc? Is there some EDID data quirk?