I have a cheep LED flashlight. It consists of five white LEDs, one of which has started to blink. I'd guess about 10-20 times a sec or so, with a constant frequency, as far as I can tell. The odd thing is that the LED's are all wired in parallel and the others are working fine. The little PCB is in rather poor condition, but I don't think it is a slack joint, as the effect is constant no matter what I do to it.
What kind of failure mode can cause that? What causes the oscillation? The cirquit is as simple as it gets. Two AA batteries in series connected to the LEDs. There isn't even a proper switch. The flashlight is turned on and off by losening or tighening the two parts of the housing that are screwed together (which causes the positive pole of the battery to push against a pad on the pcb).