But taking this into consideration the basic diyer would probably stated here they changed the system battery anyway
So sometimes being able to do many things makes no difference
It could be anything , but as said , check fuses , check power outputs , take the plunge maybe and change the battery aswell
Have fire extinguisher ready incase you get something wrong but usually small.pcb like that shouldn't be that bad as long as you don't use foil paper as a fuse