April board does not power with external power supply

I have a april board, it power up (IMP is blinking) when I used the USB adapter.
When I connect my own +5V to either the P+ or the Vin input, the IMP is not blinking. The onboard DC/DC is creating its 3.3V ok (comes out on Pin 3V3).
I have two boards that do the same thing.
Any help?

Silly question, but have you changed the jumper over to the BAT position?

Actually no, since I power it directly to the Vin pin on the edge connector.
I found that the 78L05 was the issue. It only provides 100mA, not enough for the power burst when he imp want to do wifi. With a 7805 it works fine now.

What voltage is your source? The onboard switching voltage regulator is way more efficient than a 7805, and if I remember it correctly, you can power it with up to 17v.