[activate HDMI wheezy 7.5]

I am running cubitruck wheezy 7.5 from 2014, Kernel 3.4.104 for over three years as homeserver with VGA display.
How can I activate HDMI for a new display. (I cannot reinsall the whole system, growed up for all the years)

I already changed the settings in fexfile:

[disp_init]
disp_init_enable = 1
disp_mode = 0
screen0_output_type = 3
screen0_output_mode = 6
screen1_output_type = 3
screen1_output_mode = 6

also changed fex to bin and reboot, but no HDMI-output

Can anybode give me a hint?