I attacked the failed unit and it appears to be potted with something 'softish' - rather like the consistancy of hardened putty (for window glass). Proably a polymer resin and I would bet that it is this substance than makes all the smoke.
The amount of blackening inside the instrument extends 3 to 5cm in all directions and is an absolute
to remove, it resists water, alcohol and propanone (acetone) equally. Water, cotton buds and a lot of scrubbing get if off eventually.
dave