i semi-successfully assambled my xmas present the MinyPI 3.5. Soldering went fine and card was flashed too.
However i do have the following issue:
1) first boot no SD-Card -> white screen then turns off after 3 secs (i think its normal?)
2) flashed SD Card -> booting now battery no issues, (however i hadnt soldered the L/R buttons not speaker then)
3) Soldered speaker and buttons and did the final assambly
4) POwer on -> white screen -> 2 secs (sometimes one sec) it powers off

5) Fully charged battey until LED was green -> same status
6) Booting on USB-C no success, still powers off immidiatly or after 2 sec latest
7) disattached battery board (dont know just for safy if it can remain attached?) boot on micro USB dirctly -> Boots up with boot screen
What could be the issue for this, i measured all pins and dont see an obvious issue connection per all pins seems fine