PWM Signal PIN M1 is on Ground

[Wolfes]

Dear Board Members,

my name is Wolfgang ... flying Copter in couple of years with many different bords like MultiWii, Armo-O-Kopter, Openpilot, APM, ...

This week i become a used AutoQuad board from a other pilot and himself its also by used.

Now the problem is, on the board is nothing work (no red light). First i change the recom to original 7805. When power connect (adjustable power 500ma/12v) the 7805 (near the GPS) going verry hott also the voltage regulator to 3.3v.
In addition check i came to notice the signale output pin M1 has 0,9 ohm to ground.

I think this is not normal and the reason of the problem. I search a resolution to the problem i a not able to find a connection schematic about the STM32F4 Cortex.

Can anybody check the M1 signal pin ohm to ground, ore has a connection schematic plan of the board?

Thanks verry much.

Wolfes

[JussiH]

The heating of the 3.3V regulator and the Recom (it should be a Recom, not a 7805) going hot and the fact that the power LED is not coming on all points to one problem: Dead STM32F4 - this can happen if a signal pin is subjected to a voltage spike.

It sounds like you know your way around electronics. Provided the board did not suffer impact or reverse voltage damage there is a good chance you can revive it by replacing the main STM32F407VG Microcontroller.

Start by removing the main STM32 and clean up the pads carefully. Then measure if there is still short from M1 to ground...if the short is still there, track it down and remove it...but M1 signal pin goes straight to main MCU, so a short to ground can pretty much only happen at the servo connector or MCU side.

But I am betting the short will be gone after removing the MCU. If it is, power up the board on the limited supply (8V, 200mA should be enough) and see if the Power LED comes on. If it doesnt, check that there is supply voltage coming to the 2 recoms and that 5V is coming out.

If the Recoms are not getting Vin or putting out 5V or still getting hot after removing the MCU, It could point towards the board having sustained reverse voltage damage that will kill recoms and possibly also damage the board. You can try and replace them, but a high current reverse voltage event is likely to damage or burn out an internal Vin supply trace and possibly cause other damage, so verify that there is continuity from Vin to Recom input pins before attemting to replace them.

[aBUGSworstnightmare]