I have a pi model B being used to read from a rfid card reader.
After a week or so of continuous use, it powers down and the red light goes dim;
If I check the voltage across TP1 and TP2, I get 2.615 volts;
However if I measure the voltage across the supply its giving over 5 volts;
If I power cycle, it comes back up, and the TP1-TP2 measures 5 volts again.