Definitely the chip.
Qlg1 was attached to a u3s and was working fine for weeks. Then it suddenly stopped, u3s still running, 5v very well regulated supply. I initially thought it was the rf chip but I probed the input to the chip from the rf chip and it was definitely receiving signals from the rf chip, the output however was a constant 2.34v or something around there on both outputs pins 3 and 8. Consequently pins 4,5,12 and 13 were fed a constant voltage which meant that the green led was constantly on and the yellow led never lit. Removed chip without damaging the board, soldered in a socket, replacement chip and all was good again and still is.
No voltage spike or incorrect voltage applied, it just failed, must have been an internal fault, I destroyed the chip to remove it from board so didn't check it further. Just one of those unexplained failures, though I must say that I haven't had any other IC's from anything else I've built fail so one chip isn't bad and nothing else was damaged.
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.