I saw hambone1216's post on metal halide lamps, and it made me think of the ballasts for these lights.
I installed (6) 400W metal halide high bay lights back in 2005 (about 3 1/2 years ago). Four (4) of the lights stopped working. We tried new lamps, but they still didn't work. So, we replaced the ballasts. This fixed the lights, but it's awfully expensive.
I have two questions. One, how long should a typical metal halide ballast last? And two, do you guys typically get a ballast rebuild kit? Or do you troubleshoot the light, and replace just the capacitor or other components in the light fixture? I've always just replaced everything, but that's usually after the lights been in service for a MUCH longer time than 3 1/2 years!