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I bought this adapter: www.delock.de/produkte/F_697_MHL_65337/merkmale.html in the hope that it would send native 1080p video from my HTC One (M7) running CyanogenMod 12.1 to my Benq GW2265, which is a full HD monitor. But it won't. Somehow the adapter or the phone seem to get the impression that the monitor only supports 640x480@60Hz, so that's all I'm getting. I've also tried it with two different models of HP Compaq HD monitors - same result.

Now if I plug the same phone and the same adapter + a DVI-to-HDMI adapter into an HD TV, I get 1080p@25Hz output, so I know the phone and the MHL adapter can both reach that resolution just fine. It's just that these computer monitors for some reason aren't being seen as devices capable of displaying resolutions that high.

From what I've read online, one possibility would've been that the monitors were not reporting superior MHL-compatible resolutions like 720p@60 or 1080p@25/30 as being supported via their EDID blocks. But as it turns out, my Benq really is reporting 720p@60 as an available standard resolution in its EDID block (though not 1080p@25 or 30 Hz because computer monitor refresh rates don't go that low). So I still don't understand why the phone won't send 720p@60 to the monitor rather than 640x480@60.

Per some instructions found online, I've tried reflashing my monitor's EDID - figured maybe if I moved the 720p@60 value up the list so it gets reported as the first standard mode it might register at the MHL end. No dice, though: the monitor's EDID ROM is write-protected and I don't know how to disable the protection.

Then I found out the Android files/devices having to do with MHL output were sitting in /sys/devices/virtual/graphics/fb1/ and that some people had gotten results by sticking a value of 4 (corresponding to the 720p mode) in the video_mode file after connecting the adapter and monitor. Again no dice - the file seems to get immediately reverted to containing a "2" and there is no change in the image I'm seeing on the monitor.

I'm almost giving up here. Can this even be done? Would there be any use in getting an additional DVI-to-VGA converter to try to go through the monitor's other input? Or is there something else I can try?

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That idea of adding another converter and going digital-to-analog seems to be one of the ways of getting this kind of setup to work. I added a simple passive DVI-to-HDMI adapter after the above MHL converter (e.g. http://naplestech.com/images/dvi-to-hdmi-adapter.jpg) and then continued with an active HDMI-to-VGA converter, namely this: http://www.sandberg.it/product/HDMI-to-VGA-Converter

Plugged the whole converter-adapter-converter chain into my phone at one end and into the VGA input of the monitor at the other and presto: 720p@60Hz right away.

Now both active adapters have extra USB inputs allowing them to be powered from some source other than the phone, but surprisingly the whole chain can also be powered by the phone alone and will still work. (Everything I've read online about MHL v1.0 says the MHL adapter itself will not work unless powered from an external source, but somehow it seems that's either not true or was not referring to the adapter and the video output but rather to supplying power to the phone while it works in this way.)

Caveats:

  • Sometimes while streaming the monitor image goes blank for a second or two and then recovers; this seems to resolve as the adapters heat up or somehow "settle in"

  • Sometimes at the beginning of a usage session the monitor image turns into white noise whenever starting a video or launching a game and does not recover until some part of the chain is unplugged and plugged back in. Not sure what causes this but again it seems to resolve in time, through some sort of "settling in".

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