Odd problem -- board shutting down during kernel startup (now resolved!)

[Jules]

I'm not sure what's going on exactly (I don't currently have a suitable cable to hook up to a uart so I can see what's happening on the console), but I'm experiencing an odd problem with my A13-WIFI.  It starts to boot up fine (if I use the default image, I see the android boot screen, which briefly changes to the android logo sometimes but not others), but after about 5 seconds appears to shut down.  At the same time it shuts down, the 3.3v pins in all the GPIO connectors change voltage to about 0.7v.  I initially thought I'd overloaded the power supply by hooking up some external logic to one of the +5v pins, but the 5v power supply is still working fine which seems to suggest that this is not the cause of the problem.  Anyone know what might be going on?

[Jules]

An additional data point: the 'RESET_N' line in the GPIO-1 connector is going to 0v at the same time the 3.3v supply drops to 0.7v and the processor halts (presumably because something's resetting it...).

I understand from other posts that this line is connected to the PWROK output signal from the AXP209 chip.  Does this mean that the AXP209 is detecting some fault with the power supply?  If so, what kind of fault is it likely to be detecting?  I have a 12v 2A PSU hooked up, which should be more than capable of supplying the power required by the board, but I'm not certain how well regulated it is... is the AXP209 picky about working with noisy power sources?

[Jules]

Err. Answering my own question, yes it does seem to be objecting to a noisy power supply.  Switched to a different one and everything's now fine.