Problems with external 5V supply

[gregory hermant]

Hi Richard,
When the board is supplied by an +5V external power supply you need to 
press the blue push button to powerup the board.
If you want to circumvent this you can put a jumper on the MAINCH header 
in order to start the board automatically.
Regards
gregory

Richard CURNOW wrote:
> Hello,
>
> I'm having problems supplying a SDK board (V11) through the barrel jack.
> I've tried not only a couple of "wall-wart" type supplies (both rated 5V
> 5A), but also a bench supply in the lab.  With the lab supply, we also
> tried varying the voltage in roughly 0.5V steps from 3 up to just over
> 5.  The symptoms were the same regardless.
>
> What I'm seeing, for all these 5V supplies, is:
>
> * the LED between the barrel jack and the OTG connector is lit
> * neither the green "User LED" nor the blue LED on the back panel ever
>   become lit
> * a voltage around 4.3-4.4 is present on the exposed metal of the jumper
>   by the words "EXT PS"
> * pin 1 of the JTAG header, which should be 1.8V, is reading 0V
> * the machine at the other end of the console cable _is_ detecting the
>   USB device - in other words a /dev/ttyUSB0 is created by udev – so the
>   FT232RL and the other USB connection are powered
> * however there is no text displayed in minicom – no boot messages, at
>   all
>
> In contrast, if I power the board through the OTG connector
>
> * all 3 of the LEDs become lit
> * 1.8V is visible on pin 1 of the JTAG header
> * the boot messages are visible on the console connection and a working
>   root shell is reached through minicom
>
> We're stuck for what to try next.  Has anybody ever seen a similar
> problem and fixed it?  Or is the board faulty?
>
> The other point I've noted is that the reset push-button doesn't result
> in a successful reset.  The root shell becomes frozen, but nothing else
> happens.  Neither does a "reboot" command typed into the shell do
> anything.  Is it possible there is a problem around the reset handling –
> which is avoided with OTG power because of the logic that limits the
> initial in-rush current?  Maybe the AB8500 is not starting up (hence the
> lack of 1.8V output to the JTAG header) ?
>
> Any ideas would be much appreciated.
>
> Richard
>
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