Petzl MYO 3 users have reported some reliability problems with these headlamps in postings over at UKClimbing.com.
According to some users the wire inside the bulb housing can work loose and cut the juice to the light. Seems, according to two users, that the wires are pressed into metal contacts rather than soldered in place. I don’t have one to dismantle and check but it sounds quite plausible. Post a note if you’ve had a similar problem. I’ll be writing to Petzl to ask if this is a common complaint and if they are taking steps to correct it.
For the record, the MYO 3 is a hybrid light with a halogen bulb to gived a long-range beam and a set of thee LEDs for close-up work. In most cases it’s been overtaken by the newer MYO XP and Tikka XP lights or the Princeton Tec EOS, which give similar long-range beams with a far better battery life than the Halogen-bulbed MYO 3.
UPDATE: Petzl has written back to me saying they aren’t aware of the problem and urging users to return faulty lights. Their response is posted here.