faulty voltage regulation on t3.6

[xam]

I'm experiencing some problems with the voltage regulation of my teensy 3.6.
I used it as the brain of my diy cnc machine and it worked all fine. Until today.
The pc doesn't recognized it and i first thought it would be the usb jack's fault but it's definitely some part of the voltage regulation.
So i tested a bit around and noticed, that it is getting really warm (not happened before), especially a 3 pin component named "AN .w69" near the usb jack.

Google was not able to get me any information about this little thing.
I powered it with a LM7805 to do some measuring and a fact is that the 3.6 is pulling a current of 220mA and the voltage at the 3.3V pin is dropping to 1.76V.

Here is what i think happened:
I had common ground between the cnc power supply an the teensy's gnd (powered through usb), without using a safety resistor to limit a possible high current.
I never measured it before, but my multimeter says, that there is a voltage difference between the usb and power supply ground of 0.83V.
It could be possible that there was flowing a to high current that killed some part of the voltage regulation.

Maybe someone has an idea what has been damaged and how to rescue the 3.6.
To be mentioned: The programm actually running on the board is putting on the internal led when it's powered up. And the led glows very dark if powered up. And, quick after powering up, it's still able to upload code.
So i think that the rest is still working.
Thanks.

 

[GremlinWrangler]

Does sound like a regulator issue, and a naked T.36 shouldn't be pulling that much. Guess would be that something in the power chain has indeed been upset by the cross feed between your two power 5V supplies if that was allowed to flow through the board.

The schematics are here
https://www.pjrc.com/teensy/schematic.html
Basic idea is probably to dry and isolate the 3.3V reg and possibly filter components if they are at fault, but the surgery to do that will be a little bit interesting given the scale here, and I'm assuming you still want USB to work, so those wires still need to work.

It is possible to write code that configures things in ways that draw high current and fix for that is pressing and holding program button while you plug it in to prevent user code running, but this seems less likely here, since at 220mA the onboard reg should still be fine since it's rated for 250mA on top of the existing Teensy draw.

 

[xam]

Thank you for your reply.

I tested to prevent my code from running but it didn't helped, as you assumed.
The scematic is very helpfull.
The parts named there a different to those installed on my t3.6 but they are doing obviously the same.
LP38691 is a 66HVH L120B on my board.

It looks like it's very easy to bypass the the regulator by powering the t36 directly through the 3.3V pin.
But i have to order a suitable regulator first
The diodes are rated for 1A so i think the parts could be faulty are the fuse, ferrite or the regulator itself.

I will try to bypass the regulator first and if this works, to change the named parts.