I had the same prob. kept getting called to a shop that had the halogen bulb "black-death". After three trips to replace bulbs, the culprit turned out to ber a very small drip that made a line-neutral, or a line-line fault at the breaker. It was a bolt missing on the hub. I noticed the water, or mineral stains across the busbars. A little dab a goop, and I was through [Linked Image]