Can be a hardware issue. Boards (at least some revisions) have small design 
"feature" that will make them unusable with some HDMI adapters.
I have A6 revision and a Delock 
63457<http://www.delock.com/produkte/G_65347/merkmale.html?setLanguage=en>HDMI 
adapter.

Now the HDMI adapter gets it's power from HDMI connector (+5V) through a 
resettable fuse PTC (noted RT1 on schematic, the yellow component near USB 
host connector). This excellent feature will protect PM (the 
*TPS65217*<http://www.ti.com/product/tps65217c>) 
against cheap chinese adapters or enthusiasts bad behavior through HDMI 
interface. The problem is the fuse which is under-estimated, on my board a 
100mA PTC is mounted.

Since *TPS65217* <http://www.ti.com/product/tps65217c> can handle a lot 
bigger, just replace the fuse with a 250mA one and you'll be ok. Better, 
remove the PTC and power the HDMI directlly through +5V main supply since 
there is the same +5V regulated and the kernel will anyhow put the device 
in standby if too long inactivity on keyboard or mouse will be detected.

As a rule of thumb... if the PTC gets hot, the HDMI adapter tries to draw 
more power that fuse can handle. The voltage will drop under 5V and HDMI 
adapter will goes grazy... you will have a short image at boot time, then 
nothing. The board doesn't allow me to upload some pictures about issue.

Regards,
Edouard Gora, YO3HCV

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