LG Help-line said probably a failed magnetron, but since out of warranty,referred me to an authorized LG repair service. They wanted $79.95 service call to come out & diagnose problem. I ordered replacement magnetron for less than cost of a service call, Plus the part was delivered next day! Works like new again. Happy wife = happy life!
Notes for DYI-ers:
1.Be careful removing over the stove microwaves--get help,they are heavier than you think.
2.Unplug microwave for 48 hrs, carefully disconnect capacitor leads, and CONFIRM capacitor is discharged before doing any electrical repairs in a microwave~!!