(Some of you might have already know how to do this, but this simple info will still benefits other users)
I search the forum & found little information on this topic, hence I decided to write one myself
Our Z Ultra use MHL 1 (Not MHL 2 or 3) & when I first connect it to my TV, the display is being fixed at: 1080/24p
At 24 frames per second, I can watch movies & videos without issue. But I noticed a minor lag when I open apps & the whole phone UI just feels slow....
Things get really worse, when I try to play games via MHL output on my TV (I use dualshock 3 controller + sixaxis app)
The lag is killing me & made most 60FPS games unplayable, I even tried 30FPS games & still notice a minor input lag.
For gaming, basically we need 60FPS output, 24 or 30 FPS is not smooth enough.
With some simple tweaks, we can force the Z Ultra to output 720p at 60FPS (We sacrifice the 1080p display quality in order to achieve a smoother 720p output)
First, you need to access the service menu by dialing *#*#service#*#*
After that, select Service tests, scroll down to TV-Out Test & select it
Now connect your phone to your TV via MHL cable/adapter & make sure that it's properly connected.
select Video format
There are a few options to choose from, for gaming we need 60FPS so we choose 1280x720p@60
After that, disconnect the MHL adapter from your phone & then reconnect it again.
The phone should now output 720p at 60FPS to your TV.
Note: If you restart or shutdown your phone, you will need to access service menu & do this simple workaround again.
This should work with other Xperia models as well, as long as you are able to access the service menu & change those settings.
Hope the above info helps
UPDATE: I notice my MHL adapter (3rd party) stops charging the phone after I change the TV output resolution.
If your adapter is doing the same thing, just disconnect it from your phone.
Plug in your microUSB wall charger & let it charge for around 30 seconds.
After that, connect your MHL adapter again to your phone, the problem should be gone.