STM32F4 Discovery Board external power problem

Hi,

I am trying to feed my Stm32F4 Discovery with 5v in pins. I have tried to feed it with ESC's BECs , PDB or with voltage regulator and Li-Po battery but I am still facing with problems.

The problem is that when I try to make PWM generation in tim4 in all 4 channels, there is no problem. but if I try to use tim3 4 motors works when it is connected with Pc via microUSB, when I feed stm externally just 2 or 3 of them works.

I can not understand reason of this problem and how can ı fix it. Now I can use tim4 and be aware of this problem but I wonder the reason of problem and is there any other pins have this issue ?