In reply to Gob_Stopper:
I took my old Petzl Myo 3 appart with a knife to find out why rather than send it back, not being satisfied with a random malfunction from something which I think you ought to be able to depend upon, and I discovered that the wires inside are just pressed into 2 little vertical metal slots, with two gaps in the wire insulation to make the contact. All one of the wires inside has to do is move a little bit, and you get a dodgy connection.
Why Petzl thinks it's okay to charge upwards of 30 pounds for this quality of product I don't know. I was going to post a picture on flickr and send it into the magazines and post on outdoor mesage boards, but i've lost the relevent parts in my headtorch.
I'm thinking about doing the same with thier cheapest Myo though, and soldering the contacts after I have done. I thought rest of the wiring inside my Myo 3 was pretty cheap and brittle though, and a little bit difficult to bend about much before it broke and needed replacing so you could solder and have a working headtorch.
They're poor quality overall in my opinion, it doesn't sound like the design has changed if malfunctions are still ocurring on Myo headtorches.
I was pretty annoyed actually and still am a bit, and should probably get my act together and send a picture of the wiring inside to Petzl and ask them if they're going to make any changes to the design. If enough people do perhaps they will do...
Cheers
Tim