Model-Specific Differences
Fragment of a discussion from Talk:R-Pi Troubleshooting
There are other places. The red LED is no longer directly connected to the 3.3v rail, but driven by the RST output of an APX803 supervisory circuit. As a consequence, a blinking red LED on the B+ is not a direct consequence of a brownout, but a warning that the 5v power rail is dropping below 4.63v. I'll add a sentence to that effect.
