Clara HD Kobo Clara HD revival - not fixed after new battery and firmware

[einked]

Hi,

got a fun project from a coworker, her Kobo Clara HD (RevA) has died some time ago.
Screen stuck on the last book cover she was reading, non-responsive totally.
Plugging in it gave some life signal, blinking at the power button, but only 2 blinks i think then noting.
I ordered a new battery as the old one was definitely dead.
New battery arrived, popped of the back, plugged in the new one, same reaction...
I started reading about firmware issues with the HD, requested the Clara HD firmware here in the other thread, got it really quick what i really appreciate!
Still, despite some improvements, the HD is still dead.
Now with a new sd card and latest firmware i get 2 long blinks, then 12 short blinks and then the front light lights up, but no other change.
I left it like that for 30 min, nothing changes, the old book cover but with front light. Not responsing to touch or anything.
Does anyone has any idea what else should i try? i reconnected the screen ribbon cable, no change.
The HD is in a great condition, would be a shame if it could not be resurrected.
Thanks!