1.8 Rotor button fried

[minipete]

Off on holidays last week in my Giulietta and it conked out 400km from home with a fried rotor button.  Rescued by my brother and a trailer so all is well but I can't understand what would have caused this.

The cap looks fine but the contact on the rotor for the centre (coil) lead has been arcing and has eaten away the plastic and eventually melted the locating post and the rotor started spinning.

It has an electronic distributor (Bosch I think).

I'm not likely to trust it until I can find out what caused this.

Could it be the control unit for the sensor?  I assume this is the box screwed to the body under the coil?

Any ideas?

Pete
83 Giulietta

[minipete]

I put a new rotor, cap and leads in today and it seems to run fine.

I'd like to find out what melted the rotor before I trust taking it anywhere.

Pete