Light rig problem - only 4 bulbs of 6 lighting up

[d3rryc]

Yes, it's been a bumpy few days for the Cannon fish tank. After two pump failures in two days and the loss of a green monti to agents unknown, I noticed today that two of my T5 bulbs aren't coming on (ok, I'll stop whining now - Sherri's the one who's had the REALLY crappy week). I'm running a Tek Light with six 48" bulbs. All of the bulbs are less than three months old. The attached graphic shows how the two outer lights are wired together as a unit, while the four inner lights are wired together as a second unit. The two bulbs in the inner unit marked with a red X aren't coming on. I swapped a working bulb with a non-working bulb and verified that the problem is with the fixture, not the bulb.

Can anyone tell me what might be causing this and how to fix it? I'm not a total electrical noob, but I've never cracked one of these light rigs open before, either.

Thanks!
Derry

[alton]

Bad ballast or sometimes depending on the wiring two lamps are run in series with the ballast, so if a wire comes loose both lamps quit working. Sounds like you are going to have to send it back.

[d3rryc]

Unfortunately, I don't think they'll take back a rig that's almost two years old... ; )

[ErikH]

Are those actinics? It sounds like a bad ballast. You should be able to call the manufacturer and order another one.

[mharmon]

Check out what happened shortly after Chris lost two of his six T-5s...

http://maast.org/forums/showthread.php?t=48448&page=9

Be careful!

[brewercm]

Bad ballast or sometimes depending on the wiring two lamps are run in series with the ballast, so if a wire comes loose both lamps quit working. Sounds like you are going to have to send it back.

I would think more likely the wiring issue, if they are all on the same wire series that would mean they are all on the same ballast. I doubt a ballast would only work two of four bulbs if it went bad. Most likely you'd loose that whole chain of bulbs for bad ballast.

[d3rryc]

So it turned out to be a bad bulb after all. When I swapped out one of the non-working bulbs for a working bulb, I had the bad luck of swapping a good bulb for a good bulb. I simply got lucky while troubleshooting the rig after taking the reflectors off and loaded up four good bulbs into that middle set. After some more noodling, I figured out one of my actinics wouldn't fire up, and that was preventing the bulb paired with it from lighting up, either.

Note to self - when two neighboring bulbs fail to light, swap BOTH bulbs to confirm that the fixture is working, and go from there.