Unable to turn SM-T560 on

Hi,

I have a SM-560 with a non-working battery. I changed the battery and was able to turn it on and succesfully complete functional tests. Unfortunately I tried to connect the cable (see picture) again. I then noticed, that it turned off. Since then I am unable to get it back working.

What I have tried already:

• Holding Power Button + Volumne up + Home-Button and several combinations
• Disconnecting LCD, Digitizer, Battery
• I have also verified that the battery still is fine.

What can I do next?