A little less than a year ago I bought an outside “barn light” LED fixture and it suddenly quit. No warranty because companies mentioned in the paperwork can’t be found today...

However, I pulled it and found the power supply had quit putting out the DC voltage. I have found similar replacements but at 30 bucks (the light only cost me 30) it just don’t seem worth it, and as usual I’m curious in my jackleg way if it might be a simple part fix. Of course it’d be nice to have a schematic but I can’t find any info on the net...so...just tossing it out here to see if anyone can point to some possible areas that I might look into this piece...(I just hate to throw anything away until it’s absolutely time LOL)

Thanks for any ideas.
(The pic of the component side looks “fuzzy” because originally the whole thing was covered in a block of some flexible plastic that I chipped away at for a couple hours lol)

 

If a schematic isn't readily available, the normal procedure would be to trace the circuit and create your own. If you can do that, someone might be able to help you.

The good thing is that there don't seem to be any black blobs of encapsulated circuitry which usually mean it's not worth trying to repair. Do the 8 pin packages have standard part numbers? The 3 pin SOT-23 type devices usually have a marking that can be cross referenced to a standard part.

 

Thanks for your helpful info, but it’s a bit above my “jackleg” ability LOL (yes I can look things up and learn but I’m getting older quicker and my learning abilities are getting harder and harder)

I was just looking closer at the parts and getting ready to try and research circuit board numbers I see but I think I’ve seen where these cheap products aren’t readily documented...in the meantime, in my usual “jackleg” way again, I am going to power up the board and start probing around with a meter and see if I might find a problem area.

In my warped way of thinking (simplified) I feel like power supplies like this would have a lot of parts, flows in common, and that maybe some of you guys that KNOW electronics might have some idea where the breakdowns might typically occur. I found in a recent experience with a refrigerator board (unit was near new and friend bought new one and gave this to me—I just COULDN’T let it go haha) that the relays were usually a hot spot...metered then out and sure enough, problem solved. Still working over a year later...

 

Also, I tried some other “wall wart” type supplies—got one or two to work but light was dimmer on one, and the other had a “flickering”—I take it that might be why this original unit specifies OUTPUT CURRENT: 1670 mA Constant Current? Key word constant?

 

I’ve had similar issues with these cheap light fixtures. Had a goofy power surge about a year ago and took out the TV, Computer desk top power supply, the Yard LED light fixtures, the power strip protection circuit and the WII game machine. They all had the exact same items blown. 1. The Fuse, it my look odd, these were standing up like a resistor but with a piece of heat shrink tubing over them, obviously with out AC connected, use the ohm miter to check for continuity. The glued to the transformer was a MOV (Metal oxide Varistor), This is a cleaver design element in these power supplies. It senses very quickly if the load varies and will blow open (in affect a second fuse) I have found some circuits have multiple MOV’s in them. Someone else may be able to give you the math for how large, or what value to use.

I had several photos attached but could not figure out how to attach them to this response. MOV, Varistor, they come in many different shapes and sizes. one you get moving them around they may crumble then you have surely found something that needs replacing.

look up varistors, and Medal Oxide Varistors – these things blow so fast that it saves your house from burning down, and actually saves the rest of the electronics in the circuit. The funny looking yellow thing could be a fuse, sometimes they are a small rectangular box that you can pull the top off and see the fusible link. Before yanking out parts it might be good to check to make sure they are bad before destroying them.

I always have a couple of old computer boards laying around… so I scavenge some parts from those board and fixed all the devices. I think the epoxy glue is not to just make it difficult to work on the item. They did it to keep parts in place and some items tend to resonant causing interference problems so they stick them together and reduces the buzzing of the parts. The amazing thing is nearly all these parts are also inside of a LED light bulb that you screw into a fixture. (Also, the old florescent sockets crammed a lot of good parts into those sockets.) I am not a pack rate; I keep valuable parts made from rare earth medals. No sense sending them to the land fill. Hope you fix it or at least figure out what the problem is. I tend to figure out the problem, then throw the stuff into a box and say, “someday.”

RMG

 

I’ve had similar issues with these cheap light fixtures. Had a goofy power surge about a year ago and took out the TV, Computer desk top power supply, the Yard LED light fixtures, the power strip protection circuit and the WII game machine. They all had the exact same items blown. 1. The Fuse, it my look odd, these were standing up like a resistor but with a piece of heat shrink tubing over them, obviously with out AC connected, use the ohm miter to check for continuity. The glued to the transformer was a MOV (Metal oxide Varistor) This is a cleaver design element in these power supplies. It senses very quickly if the load varies and will blow open (in affect a second fuse) I have found some circuits have multiple MOV’s in them. Someone else may be able to give you the math for how large, or what value to use.
I had several photos attached but could not figure out how to attach them to this response. MOV, Varistor, they come in many different shapes and sizes. one you get moving them around they may crumble then you have surely found something that needs replacing.
look up varistors, and Medal Oxide Varistors – these things blow so fast that it saves your house from burning down, and actually saves the rest of the electronics in the circuit. The funny looking yellow thing could be a fuse, sometimes they are a small rectangular box that you can pull the top off and see the fusible link. Before yanking out parts it might be good to check to make sure they are bad before destroying them.

I always have a couple of old computer boards laying around… so I scavenge some parts from those board and fixed all the devices. I think the epoxy glue is not to just make it difficult to work on the item. They ddi it to keep parts in place and some items tend to resonant causing interference problems so they stick them together and reduces the buzzing of the parts. The amazing thing is nearly all these parts are also inside of a LED light bulb that you screw into a fixture. (Also, the old florescent sockets crammed a lot of good parts into those sockets.) I am not a pack rate; I keep valuable parts made from rare earth medals. No sense sending them to the land fill. Hope you fix it or at least figure out what the problem is. I tend to figure out the problem, then throw the stuff into a box and say, “someday.”

RMG

Interesting stuff...thanks! As I read that I found something resembling a MOV—it was covered in shrink wrap and once I cut it away revealed what looked like a resistor standing on end...the board says R18 like other resistors but why would this one alone be wrapped? Hmmmm

 

Or maybe this one? Labeled as CY1

 

and HERE is that CY1 ...I believe it’s a JNC varistor JN472m with the numbers of
440-250 and 400-2F on it...
On meter shows open...

 

If you're anywhere near a DirecTV outlet - or Xfinity, go in and ask for a 12 volt power supply from a returned receiver or modem. They're typically rated upwards around 5 amps (5000 mA) and should be strong enough to support your LED's. I go there from time to time and ask for one just because I'm passing by. I always get one or two of them. Being that they're for a reliable system like a modem or a satellite receiver, they're not the cheap ones. They're built to do the job. The cheap ones are just built.

As for LED's requiring constant current, since I know nothing about the light you have, I can only say that LED's are current controlled devices. For instance, take a 12 volt power source and a white superbright LED. Typical forward voltage on the LED is 3.2 volts (from what I've experienced). 12 volts minus 3.2 volts (forward) leaves 8.8 volts that have to be dealt with. You'll need a resistor for that. You also need to know the recommended current to run the LED at. The LED's I'm thinking of typically run from 5 mA to 20 mA. Being "SuperBright" I like to run them on the low side. I'll pick 10 mA. So 8.8 divided by 0.01 = 880 ohms. I'd use either a 1KΩ or two 470Ω resistors in series. The two resistors in series would equal 940Ω, which would give me a current of 9.4 mA. You would not be able to see a difference in brightness at that small change. Using a 1KΩ resistor would give me 8.8 mA. Still plenty bright. In fact, maybe brighter than you'd want.

[edit] 10 mA at 8.8 volts = 88 mW (milliWatts). A quarter watt resistor would be perfect to handle the heat generated in my example. [end edit]

But since you're talking about a barn light - I'm sure there's an array of LED's giving you the light output you want. If you could give us more details on the LED's themselves we could help you figure a good workaround to get it up and useful again. As for the old supply, I'd mess with it but only because my jackleg is bigger than yours. I'm no expert, but I'd be pulling things off and testing them to see if they're the failure point. Also keep in mind that sometimes a failed component may drag down several others with it. Not likely if a fuse blows or if a resistor goes open. But failed caps, transistors and diodes can pull other things down. Given how much trouble they went to just to prevent people fixing these things makes me wonder if they don't want people copying their design - or if they don't want the knowledgeable from seeing how poorly their PS was designed. But with how easy it is to come by PS's, I'd just look to replace it. Only if I were VERY bored would I bother to create a schematic to work from.

I DID modify a PS from 12 volts output to 13.8 volts. It's sitting in my garage keeping an older car battery charged so that when I'm out there I can play a car radio. Stored batteries should be maintained for voltage. Otherwise their plates can sulfate and the battery can become useless. I've had a few SLA's (Sealed Lead Acid) go bad because I didn't keep them charged.

 

LOL...thanks for all the useful information. You may be a bigger “jackleg”, but you “know” stuff too. (All that figuring and stuff HaHa) Seems as if at my advancing age the things I once thought fairly easy and memorable, are becoming not so—case in point, earlier after I’d pulled the MOV I then pulled the other thing I suspected which looked like a resistor turned on end and covered with shrink. It appears to me like it could be a fuse resistor due to where it’s located (there are three others that are similarly located next to certain components but they are not wrapped and are a different color) I had to look up the color bands, and luckily the net now has calculators for them, but I’m still not sure I saw the colors correctly. (I have a “color deficiency” problem I was told many years ago, but not color blind) I think I came up with a .47 figure—seems awfully puny? But I guess that would be good if protecting. I think it metered very low, if at all. After RMG’s post above, I started leaning towards that and it seems logical to me that this thing would have more than one protector—how I came to that I don’t have a clue, but that’s “jacklegging” LOL.

Kudos on the used power supplies—I’ll check in with my local Xfinity and see.

I’ll have to take another look at the LED. IIRC, I was surprised to see it looked like a single piece instead of several in a group but I may be wrong. From what I read on the cover and info on net, it’s 1800-odd lumens,
Output voltage is 12-24vdc, and 1670mA constant current...

 

Just for the record.

MOVs do not “blow open” or “detect load variations” as a normal design function.

MOVs are not designed to act as fuses, their basic function is to “absorb” overvoltage.

 

Just for the record.

MOVs do not “blow open” or “detect load variations” as a normal design function.

MOVs are not designed to act as fuses, their basic function is to “absorb” overvoltage.

My experience with MOV devices in consumer electronics is that they usually fail short circuited after some overvoltage, which pops the protective fuse as well as the replacement fuse, until I discover that the MOV has short circuited. The intention is that they break down at some voltage and conduct until the power is removed.

 

Just for the record.

MOVs do not “blow open” or “detect load variations” as a normal design function.

MOVs are not designed to act as fuses, their basic function is to “absorb” overvoltage.

Thank you for the precision of your answer. I couldn't quite get the words correct when writing yesterday. "Over-Voltage" perfect word! My house had an open neutral at the power pole, talk about strange voltages... had a house full of guest, things popping and smoking, ran downstairs to hit the mains before attempting any research of the problem. We do love to watch the little squirrels running around and playing. They happen to like to gnaw on the exterior jacket on the mains, they were successful at completely severing the neutral, a good test of the grounding. When the cable guy was out to fix the cable, he jumped about 5 feet back when he disconnected the cable and had a huge spark. He packed his bags and lived to tell the story. But I lost my best ground. Less than 80 volts AC on one leg and "considerable higher on the other" led to an "over-voltage" condition that the MOV's assisted in protecting all of my electronic equipment. Even if they were PS designed. I am not arguing with your assessment (or someones assessment) but they worked! My house did not burn. Will severe voltage spikes also blow these? Or does it require a sustained over-voltage condition as in milli seconds verses nano seconds?

 

My experience with MOV devices in consumer electronics is that they usually fail short circuited after some overvoltage, which pops the protective fuse as well as the replacement fuse, until I discover that the MOV has short circuited. The intention is that they break down at some voltage and conduct until the power is removed.

This what happened in my situation. But the crumbling apart and thin crack line did not appear to be correct.

 

I am going to power up the board and start probing around with a meter

Be VERY careful if you do, because any component on about half that board could be at mains potential.

 

OK, if the failed supply was 12 to 24 volts at a current of 1670 mA, then a good place to start would be with a variable voltage supply and an arrangement to measure voltage and current. And be sure to get the polarity right, or you may buy a new light. I would start with 10 volts and see if any light appears, and then raise the voltage while monitoring the current. What you will see is that the light gets quite bright with only half the current, and at that point every small increase in voltage produces a much bigger increase in current. I would stop at a voltage that gives possibly as much as 1500 mA. Now you can measure the voltage that gives that current. If the voltage is not convenient then a resistor to drop the difference at the 1500mA current is what you need to add in series to use the convenient supply voltage. R= volts/ Ma, and the R will be in kilohms. Example: 1.5 volts/1500mA =1/100 K ohm= 10 ohms.

 

Update: the two parts I pulled off ended up being ok but I replaced them anyway. Found a 2amp mini glass fuse (covered in some kind of paint-like clay color substance) and it was blown. (It is located as the very next component linked immediately after the main line input) Replaced it, and gave a try, only to see a bright flash come from it. Ouch...

 

Yeah, sounds like replacing fuses without fixing what's blowing them isn't going to work.

 

You can start, with the thing disconnected from the mains, by checking parts for shorted circuits. A failed varister will do that. They are used to protect from an over voltage spike, but then they sometimes stay stuck in the conduction mode. Or you may have a failed switching transistor in the supply.
But really, you can check out the light part with a variable voltage supply and learn just exactly what voltage and current it needs.

 

Yeah, sounds like replacing fuses without fixing what's blowing them isn't going to work.

Yep...99 Times out of 100, but there is that 1 chance...lol...