I met the same issue with U17, after touching the PCB with my fingers (either ESD, or a short cut that modified the setting of the output voltage. I had to replace U17.
Thought so.. Ordered a new Primer 2 as starting to make some head way with this, but need a well documented / commented project to hand hold me beyond the tutorial.
I had the same thing happen with my PDA (HP iPaq 1940). The DC-DC converter always seems to get zapped first ... had to replace the part on 2 occasions after just touching the PDA while it was charging.
I think it's most likely the ESD, especially if your Primer was connected to your computer at the time and you're in a relatively dry climate. It's a good idea to wear one of those static bracelets or at least touch some grounded metal first, but I don't always get around to doing that either.