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Fluorescent tube fixture: changed tubes, changed ballast, but lights still dim!

Fluorescent tube fixture: changed tubes, changed ballast, but lights still dim!

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  #1  
Old 01-25-14, 06:06 PM
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Fluorescent tube fixture: changed tubes, changed ballast, but lights still dim!

Hi, everyone.

I have a little old light box, an X-ray table from a dentist's office. I used to use it for a variety of... well, you don't care.

The setup is two F14 T8 tubes with a Magnetek 447-LR-TC-P universal trigger-start ballast.

I don't remember the exact order in which things happened, but at some point, the lights stopped coming on completely and were just dim at both ends. I replaced the tubes, but the new tubes did the same. (And at some point in here, I rewired the cord and replaced a number of the screws that hold the sockets of the fixture to the outer housing.)

So recently I replaced the ballast with a working used ballast of the same model. Still no luck. I checked voltage at the fixture, and it's about 125–126V. No problem there. When I twist the tubes in and out of the fixtures a dozen times or so, sometimes one of them comes on partially, and sometimes they both come on completely and are fine for as long as the fixture is left on. But if I switch it off and back on again, back to the tubes that only light up faintly at the ends. I've put some little shims between the outer housing of the box and the ceramic sockets that hold the tubes, just in case they were loose, but also no luck there. Since replacing the ballast, the last few times I've tried switching the thing on there has been a sort of rattling/buzzing noise that wasn't there before.

See pictures for illustrations of all this.

I do not know a lot about wiring, so apologies if I am missing something obvious, but I've been through all the troubleshooting lists and I can't seem to figure it out. Is it possible I have the bad luck of two successive defective ballasts? Do I replace the sockets now, just for good measure?

Thanks!

So I turn it on and it's like this.


After clicking the tubes in and out of place a couple of times, it does this.


And I do it a few more times...


...and now it works.
 
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  #2  
Old 01-25-14, 07:14 PM
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If you're sure you wired the second one properly (I am having a hard time following what wires go where, but it looks like it may be wrong), then the second ballast is no good either. The filament winding is working (if the sockets were bad, the ends wouldn't light up), but it is not striking an arc without persuasion - which means the high voltage winding is shot.
 
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Old 01-25-14, 07:52 PM
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Hi, thanks for your reply. I was careful to follow the same wiring scheme that was in place (which had been in place since the fixture worked for the first two years I had it), so I guess I'll go ahead and try swapping out the ballast again.
 
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Old 01-25-14, 08:04 PM
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I was careful to follow the same wiring scheme that was in place
When you install a ballast you must follow the diagram on the replacement ballast not the previous ballast wiring.
 
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Old 01-25-14, 08:07 PM
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Thanks for your reply. The new ballast was exactly the same model as the one that was being replaced (same manufacturer, same part number, and with the same wiring color coding and schematic and everything), so it is unlikely there was a mistake in that. I'll double-check just to be sure.
 
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Old 01-26-14, 09:44 PM
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It looks like the problem may be that the tubes aren't making good contact. I would clean the tube holders with a shot or two of compressed air. If that didn't get everything working properly I would replace the tube holders.
 
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Old 01-26-14, 09:52 PM
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Are you sure it's a T8 ballast and not a T12 ballast? I know I have a fixture that does that when I try running a T8 in it.
 
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Old 01-26-14, 10:06 PM
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Originally Posted by Nashkat1 View Post
It looks like the problem may be that the tubes aren't making good contact. I would clean the tube holders with a shot or two of compressed air. If that didn't get everything working properly I would replace the tube holders.
This is a trigger-start ballast.. If the tombstones were bad, the ends of the tubes wouldn't light up. Besides, he has rocked the tubes back and forth dozens of times, which would have scraped any schmeg off the contacts.

It's the ballast.
 
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Old 01-26-14, 10:34 PM
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Could be.

I replaced the ballast with a working used ballast of the same model.
Suceva, how do you know the replacement ballast is good?
 
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Old 01-26-14, 11:27 PM
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Used isn't a way to test. Just a way to change the problem.
 
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Old 01-27-14, 02:15 AM
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Ballast

Looking at the pictures it looks like the ground wire is not attached to the fixture. I can't see where the grounds are going or coming from but if you do not have a good ground connection the lamps will not work properly.
 
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Old 01-27-14, 04:04 AM
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Meh, I know all about 'ground reflectors' and such, but if a rapid-start fluorescent fixture NEEDS the ground connected in order to strike an arc (remember, it worked fine, and then it didn't - without changing anything), then all it means is the ballast is shot, and it's probably drawing a crapload more power than its supposed to.. All the more reason to swap in an instant start electronic ballast.
 
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Old 01-28-14, 04:25 PM
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Hi, everyone. Thanks for checking in!

—Ground may have gotten loose somehow at the time the photo was taken, but usually it is secured to the enclosing metal box under the head of a nylon screw in the side.
—I'm sure it's the right ballast; the original and the new one both specify "For two F20W T12, F15W T8, or F15W T12."
—I am not sure the new ballast is working. It was pulled out of a working light, supposedly, but heck if I know what that assurance is good for. I asked the seller whether he/she was sure it had been working and he just issued me a refund, no questions asked. (Yup, it was dumb of me to buy a used one.)
—...so, now I am in the market for a brand-new ballast! Any recommendations for an instant-start model? I'll be sure to post back here for whoever's curious.
 
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