New PCBs buzzing

[natester]

I just built ~10 new pcbs (stm32 based brushless motor controller), flashed them all (3.3v only) and everything seemed ok.

7 work fine. However 3 of the new boards, when I plug them into the battery voltage ~12v, they draw way too much current (limited to 0.3A during my testing, vs 0.05A for the working ones) and the boards make a high pitch buzzing noise.

The microcontroller side still seems fine, but there seems to be something wrong on the higher voltage rail.

My question is how do I best debug these? I've tried  to isolate the buzzing component, but it seems that every regulator and diode on the higher voltage side is buzzing. Could I turn up the regulated current and use a thermal camera to identify hot components? Is there a simpler way?

Any advice is much appreciated.

[ataradov]

I would check if the buzzing comes from the way your power supply implements current limiting. It might be oscillating.

And then it is impossible to tell without knowing the design details. Generally you solve issues like this by finding a way to disconnect different parts from each other and checking them separately. For example, switching regulators may have an inductor on the output that would separate them from the rest of the circuit.

[janoc]

Shorts either due to manufacturing defects or soldering are a thing ...

[nvmR]

As suggested before, a picture/schematic may be useful.
Other things to check are whether the diodes are assembles in the correct direction, and whether you did something marginal in the design - such as minimum load requirements.

Happy debugging!

[sleemanj]

You could get a silicone tube to stick in your ear like a stethoscope and use that to narrow down where on your PCB the sound is coming from.

[KaneTW]

Use a thermal camera to check for shorts.

[Whales]

Use a thermal camera to check for shorts.

Cheaper alternative if you don't have one: spray some alcohol on it and watch where it evaporates first.

[DavidAlfa]

Crank it up to 20amps, no thermal camera or alcohol required, the crater left after the explosion will reveal where the problem was, or where a new problem is.