Ballast Issue

My friend has a 600w Magnetic HPS Ballast, it turns on runs for about 2 minutes then the light goes off for about 20 seconds and comes back on, the bulb doesn't rewarm because it isn't out long enough to get cold. It just turns back on full brightness.

It does this all day long. I felt the ballast and it wasn't very hot, just normal.

Any ideas?

I'm not sure of the brand, it's a sunlight or something, just your regular economy white ballast with a handle on top.

my cheapest guess is that it could be a loose wire (or loose bulb) so open it up & check for a loose connection.
>>> be careful!!! -even after being unplugged, the capacitor will hold voltage like a battery! enough to bite! for weeks.
next guess would be the capacitor & since that is the cheapest part ($20??).....
or wait till someone here chimes in knowing the answer.

Capacitor is bad.

Edit : Make sure you replace the cap with the EXACT same value cap. Mucho important

Edit Edit : Do you have a spare mh bulb that you could plug in and try? I have seen once or twice a bulb due that for some odd reason. Put another bulb in the same ballast and bam it works... thats kind of a off chance but I would bet its still the cap

Well I was hoping it's a capacitor..

You say youve seen a bulb do that? Did it do it on and off all day long every minute or so like that? This is shutting off about every minute or two for about 20 seconds, then comes back on lol.

How old is the bulb? Bulbs at the end of their life wont fire properly and will flick on and off.

Not sure, I'll find out.

Ya but it warmed the bulb up enough to were it wouldnt restrike without a cool down period. So thats why I stick with the cap going bad.