I recently bought a HPS system from craigslist. It came with: xtrasun hood 600w hps bulb 600w / 120v heavy noisy brick of a ballast Whenever I fire it up, the light strikes on very red at first, then it eventually warms up to the point of being very bright. After it warms up, almost all the way, it will shut off. I would say it takes about 1 1/2-2 minutes to light up then it goes dark for about the same amount of time before it re-strikes and illuminates again. The ballast has a steady hum. The bulb is used but it doesn't look like it's cached out yet. How should I troubleshoot this issue? Thanks!