(ET) E-12 Charger trouble

[Bill Alburty <willaim kc rr com>]

Last night, after mowing, I plugged in the charger, and when I turned 
the timer knob to begin charging, a loud noise came from the charger and 
it blew the 20A fuse in my house circuit. I haven't opened it up to look 
yet, and haven't plugged it in again. What should I look for as the 
problem? What tests should I do? The noise sounded like a big clatter, 
as if the core plates were vibrating unfettered.
I appreciate all advice and speculation.

Bill Alburty, Kansas City