Okay, so there's this Slimline luminaire at the pool I go to. The pool's been open since what seems like the early 70s, and there's a dual F96T12 Slimline fixture hanging in the storage shed. It's only had one lamp in it for as long as I've been going there (since around age 5). So, today I brought with me two 75w Sylvania Daylight Deluxes. After installing both new tubes, I flipped the breaker (acting as a light switch-- likely...), and nothing happened. No buzzing, no flickering, nothing.

I have a few ideas as to what it could be:

• No input from circuit breaker / switch
• Could be a switch that I can't see, somewhere along a wall. Though there is only one cable going from the fixture, and it leads to circuit breaker box (which has a piece of tape labeled 'Lights' on it), so I'm thinking that's not it.
• Could be a bad breaker, maybe? i.e., check if there is voltage coming out of the breaker box / into the fixture at all?
• Maybe one of the leads is not connected internally, ie a socket lead worked its way loose or two connected cables that are corroded?
• Maybe the ballast is failed? Though I doubt it because there is no hum, no spark, it just appears to be dead.

Okay, so now that I've listed some of the possible failure points, what should I try and troubleshoot first? What's a common failure point on these (older) Slimline fittings? Also, for context, it doesn't seem like this fixture ever had a crazy amount of use. I think it maybe went through one set of lamps before someone gave up on relamping it (someone probably only had one replacement lamp, as this one appears to be new).

Also, finally- how do I go about taking off the ballast channel covers? Do they unclip, or are there screws? Thanks you guys.

My first step would be to verify that power is going to the fixture. If it is a plug-in type, just unplug it and see if the outlet has power. Use a receptacle tester, indicator lamp, or just use a phone charger and see if it charges your phone. If not, then there is something in the way, maybe another switch, possibly even a wiring error. I would start with looking for a switch.

If there is voltage present, I would inspect the fixture. Damaged power cord? Maybe the fixture also has a switch, like one of those pull-chains. If not, then it is definitely an internal error, something inside the light. Now that can't be a whole lot of things, it could either be the ballast, or the wiring. I would check the wiring first because it is easy, make sure all the wires are connected and not hanging loose, and give the wires a tug to see if they just fall out or if they are in there good. If everything looks good wiring-wise, and the fixture definitely gets power, then it is almost certainly the ballast.

I doubt it is a bad breaker, those things rarely go bad, but yes it is still technically possible.

As to the physical construction of that particular light, I have no idea because I have never even touched one lol, but I hope this helps!

Thanks @Multisubject . The fixture is hardwired.

So I guess what I should start with is to look for a switch... there's only one place where there could be one, really, and that's behind one of the two refrigerators in the back area, no other area has a wall that's covered or blocked by anything.

I hope I just have to flip a switch... but if that doesn't work (and there's voltage going to the light, and everything is wired correctly) I might as well pull out one of my 60s Slimline strips and install it there... 

Yeah like Multisubject says check line voltage and confirm it's there and make sure all the wiring has secure connections. If there's voltage to the ballast but no life from new lamps and you checked the wiring is good, definitely the ballast.

As for the light, what kind of light is it? If if's a strip light (or a certain shop light style which is a strip light but with a pair reflectors instead on flat covers) made after the 1970s, it should have two approximately 4 foot channel covers that are held in place by two slots at the end of each lampholder bracket and two turn clips. Turn the clips 45 degrees, and slide the covers out from the slot, as you know I'm sure. Older ones can be held with wingnuts, some eight (with two four foot channel covers) or six (one eight foot single channel cover, which may be a tough bear to get in and out. If it's anything else I don't have experience with them.

The most common point of failure when it comes to slimline lights is the ballast if left too long with EOL lamps. I've replaced two recently that only dimly lit up one lamp with a pair of good lamps in each light once and couldn't light a single one at all after that.

@fluorescent lover 40 - it's a striplight with two 4ft channel covers. It doesn't appear to have any wingnuts or such, so I assume it was made in the 70s. (Definitely not 80s as this fixture trumps the ones in my basement by a massive margin in terms of build quality).

I don't think I've seen one without the turn clips or wingnuts before. The covers could also be friction fit, and just pop on and off the light with some persuasion and no tools needed to remove them. I know it's common on some of the older 4ft and under strips but I don't think I've seen those covers on anything longer. Or they could be held by screws (which I don't think so as you probably mentioned them by now if they were).

On most 120V 2-lamp slimline ballasts, each lamp is connected directly to either the hot or neutral line from the wall on the stationary end, and to the ballast’s output on the plunger socket (277V ballasts are the same, except it’s only the neutral that is fed through a socket). In order to ensure the user’s safety from the high OCV generated by an instant-start ballast, the stationary sockets are designed in such a way that power is only connected to the ballast if both lamps are fully seated in the fixture. If somebody maintaining the fixture were to remove a lamp while the fixture was still on, power would immediately disconnect from the ballast because the lamp pin must be inserted into the stationary socket to complete the circuit. The way this safety feature is implemented into the stationary sockets is remarkably simple. There are two contacts inside that connect to the lamp pin, one that connects to the incoming supply and one that connects to the ballast’s input lead. Each socket is designed the same, one is on the neutral and one is on the hot. The problem you’re describing sounds like one or both of these sockets isn’t making a good electrical connection, either to the lamp pin or to one of wires connected to it. So I would take apart the fixture and examine and/or replace the stationary sockets.

Most 8ft fixtures I've seen use either screws, wingnuts, or quarter turn fasteners to fasten the channel cover on. The ones with a split cover are a bit easier to handle compared to the ones with a full length cover.

As for what's wrong with the fixture, I think most of the possibilities has been covered, I suspect there's either no power going to the ballast or the ballast is bad though as most 8ft fixtures tend to buzz when powered on.

If there's power going to the light, the most likely would probably be a problematic disconnect socket or a bad ballast IMO.