How to replace speakers?

I have taken apart my own P7 headphones (which also have a dead channel) and can say that while the wires and solder points are accessible, the speaker elements themselves are glued in place.

So if the problem is a broken wire or a bad solder joint, you may be able to make repairs. You can use a continuity tester (most multimeters - even inexpensive ones - have this function built in) to check the wires, one of which may be broken. You should also check continuity/resistance between the two solder points on the same speaker unit . There should be a small amount of resistance (about 20 Ohms for my headphones). If there is almost no resistance (only a couple Ohms or less) then there is a short inside the speaker unit. If resistance is extremely high, or there is no connection, then the internal wire is probably broken (this was the case for the bad side on mine).

In the case of the speaker unit really being broken, both units will have to be replaced with a brand new matched pair. There is no feasible way to do repairs inside the speaker unit itself. You would have to find a pair to buy somewhere, and while I’ve found units for the P7/P9 I don’t know where you’ll be able to find units for the P5. Then you’ll have to figure out a way to remove them without damaging the housing of the headphones. Like I said, they’re glued into place so that will be tricky at best or impossible at worst. That’s the part I still have to figure out for my own repair.

Good luck if you choose to tackle that project!