Help! SPI Metal Halide Light Ballast Issue

Hello to anyone who is reading this.
I have an SPI Metal Halide Lamp that only works part-time. And most of the time it won't light up right, it just flickers away without much output.
I don't know much about this kind of lamp. My theory is that if the lamp will light properly, if even for brief moments, then the bulb itself is probably okay.
Becasue of the trouble it has getting the bulb to light properly, I have a theory that the ballast is the likely culprit. Am I close to the truth, or close to being a dufus? Maybe I'm way off.
The ballast consists of a fairly hefty transformer from "Advance" rated for 400w and 300v. The capacitor is a metal can rated for 24uf @400VAC with an internal resistanced of 1.0 Megohm.
How doe one troubleshoot this combination? I have another theory that would like to believe that it is the capacitor at fault. Perhaps it is wishful thinking. How does one test whether the cap is working properly?
I have a good Beckman multimeter and desoldering/soldering tools, a good assortment of hand tools, large and small, and some skills. Just not with ballasts and lighting. Any help, procedure, advice is much appreciated.
Thanks, Phil Simpson.
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When I was doing street lights a lot we found that 2 caps to a transformer was pretty typical. Cap boosts the start voltage so that the lamp can strike. you could have a bad cap, bad lamp or a bad transformer. I would start with the cap if the transformer is producing the correct voltage. There used to be testers that could be screwed into the lamp holder to tell ya what was wrong. Been a long time ago for me. Maybe things have changed.
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I don't spend a lot of time testing things. I just replace the ballast, capacitor, photocell if installed, and the bulb and know that the customer will have a reliable light fixture for a few years. It would not make me look good to replace one component only to have another fail several months later.
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John Grabowski wrote:

I'll second that. Also, these days a new fixture is sometimes cheap enough that it's usually cost effective to just replace it with a new one and be done with it. If the OP insists, I'm sure that he can Google for "Troubleshooting HID light fixtures" and get more info than most people would care to know.
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into a HPS similar fixture we screw in a standard light bulb. if a mogul big base bulb, use adapter to mogul. this will tell you whether your 110v is working and photoeye is working. i found this at google search for your topic: http://www.venturelighting.com/TechCenter/troubleshooting.html
and: http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLJ,GGLJ:2006-11,GGLJ:en&q=Metal+Halide+troubleshooting
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