5V pin no longer supplies 5V; other problems too

mastyskal · ‎2011-09-01

Posted on September 02, 2011 at 00:48

Yesterday I hooked up my STM32VL Discovery board as the 5V power source for a simple circuit (powering the STM32VL itself from USB). It worked fine. However, today the 5V pin is only supplying about 3V (and the 3.3V pin is only supplying about 2V). In addition, the red LED on the STM32VL noticeably dims when the circuit is connected (although it may have always done this; I can't really remember), Ubuntu no longer mounts the 33MB storage on the board, Windows 7 says ''one of the USB devices connected has malfunctioned'', and Keil uVision 4 cannot find the STLink.

Did I somehow break my STM32VL? Is there anything I can do at this point to restore it to full function?

#5v #discovery #brick #stm32vl

raptorhal2 · ‎2011-09-01

Posted on September 02, 2011 at 01:52

Before you abandon all hope, recheck the input impedance of your ''simple circuit''. It may have changed, dragging down the 5V.

Cheers, Hal

mastyskal · ‎2011-09-01

Posted on September 02, 2011 at 05:21

I'd disconnected the circuit completely and just used my multimeter on the 5V and GND pins on the actual STM32VL board, so that can't be it.

donald2 · ‎2011-09-02

Posted on September 02, 2011 at 15:26

The only component in the 5V path is a Schottky diode. It's an especially good one, and only drops about 0.3V with a typical load (the VLDiscovery board driving the max pin output current). It's good for about 500mA before starting to overheat.

Perhaps the USB port itself is the problem. Sometimes the power supply soft fuse / efuse doesn't reset properly.

Try putting the VLDiscovery on a powered USB hub to see if that changes the situation.

mastyskal · ‎2011-09-02

Posted on September 03, 2011 at 00:30

I tried an AC-to-USB adapter/cable I had and got the same results (as when I had been powering it from a PC's USB port)... I'm not sure this is what you meant, though. Which port, the PC's or the board's, has an efuse that might not've reset? And if it's the board's, how could one reset this from a powered USB hub?

Andrew Neil · ‎2011-09-02

Posted on September 03, 2011 at 00:42

The PC (or hub) port would have the fuse.