Help needed: odd voltages in Axo board

#1

Hey all, I'm hoping this message will reach some helping souls.

I was fiddling with an external box I'm building with transistors to control motors via Axo's PWM.
I added some protection diodes to my circuit so i don't know what happened but while manipulating, the board disconnected itself from the patcher.

It is now showing odd voltages when connected to USB power or DC jack:
5V: 3,74V
VDD: 2,07V

IC2 is getting really hot quickly too and the SD card is not showing anywhere although it is plugged in.
Also, when measure the voltage coming from the mini-USB connector, it shows around 4V. But with the same cable on one of my other AXO board in the same spot, I get 4,9-5V.

Appart from that, the board is working normally: the leds are blinking, the patcher recognizes the board and I can run patches, enter DFU mode, do a Firmware rescue.

Still, i'm afraid to power the board for too long and fry something else.

Any idea what is going on here? Is there a component I could change in the power regulation section that could have been fried?

thanks a lot for your help!

#2

I'm not an electronics expert, but are you completely sure you didn't:
-make any short-circuits (sometimes an accidental tiny drop of solder is all that is needed)
-put components the other way around (eg. transistors work directional, you could also perhaps swapped a pnp for a npn transistor by accident)
-not sure about this one, but could it be that you should power the motors themselves by their own power-source?

#3

Hey thanks for your feedabck.
Surely something happened, like a short, maybe a wire became loose.
Thing is I am using a 9V external power supply for the motors. I already fried one board by accidentaly mistaking a wire and plugging 9V into the VDD rail… This board is completely unresponsive
But as for the one that have odd voltages, the only thing that I see could have happenned is a short somewhere in my small transistor circuit.

So I'm not using this circuit, but I would like to try to find out which component on the board could have suffered from an eventual short and, as the voltages seems wrong, I would assume that something in the power regulation is not working properly?

#4

so it's now constantly giving the low power output although nothing is connected?

#5

I'd guess that something on the board draws too much power, more than the power supply is designed for, so the voltage drops. That's almost (but not quite) a short circuit.
Whatever is eating all that power must get hot, so if IC2 gets unusually hot, then that is likely the defective part.

#6

Yes, the board is giving odd voltages and low power without anything connected to it.

#7

Thanks for your insight. IC2 is the ARM cortex.
But if the ARM chip is the defective part, wouldn't that mean that the board should not work at all or even show up in the patcher?

#8

It is not that black and white with large chips. One part of the chip (perhaps near one port pin that got an ESD or some of that motor supply voltage during your manipulations) can be damaged, while the rest of it still works as usual.
Over time the heat from the damaged part may cause more damage in the chip, so that it finally fails completely. Or it may continue to work as it does now; one can never know. I have seen damaged CPUs run for years without problems (except the high temperature) and others start to smoke after a few hours.

#9

Ok I see, thanks for your insight.
All seems to work except the SD card that is not recognized at all.
I might check the behavior of the PWM pin that might have received too much voltage.

So basically there is nothing I could do that could repair the board?

Maybe some thermal paste and a heatsink on the ARM chip would make it last longer?

Still, if the SD card reader is unresponsive, that makes my board practically unusable...

#10

The SD card probably does not work because it has built-in undervoltage protection (it can not work reliably if the voltage is too low, so rather than damage the data the user wants to save it shuts down completely so that the user knows it is not working).
If you supply 3.3V to the SD card socket from a different source (that actually delivers 3.3V because it is not almost short-circuited) it will probably work.
But the overheating processor… that is always at risk of suddenly going up in smoke. I would use it only supervised, i.e. where I can immediately see it and pull the plug when it starts boiling or something.