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LED repair method?? works for me!


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Hi All. I have to post this to get some thoughts from the people who actually know whats going on. Tonight I made an interesting "discovery" that my or may not have been posted before. I was putting away my lights for the season and replacing bad bulbs on the old mini light strands. I was using the light tester I bought from Christmas Done Bright (LT990), which is "NOT" for LED's to find the bad mini bulbs in the strands. This year I began a large switch to LED's and also added an LED megatree and leaping arches. With this, I had quite a few M5, C6 and retro C9 bulbs/stringers fail. I had over 30 retro bulbs fail, 3 strings of M5 and about 8 strings of C6 "strawberry" fail. After fixing all the traditional "mini lights" the thought hit me......what do I have to lose by blasting these "broke" strings with this tester. Some of the strings were "half-string dead" and others were full on dead. As far as I read so far, they are junk, but I was going to save them for future hope anyhow. WELL.........I hooked up the first string of half dead C6, pushed the big red button, and boom......fixed. second string....fixed.....third....yep. Then I tried the M5 full failure string.....fixed. Then I hooked up 5 of the bad C9 retros and blasted....4 came on. Hit it again and the fifth lit. So far I have 5 retro c9's out of 5 tested working again, the one string of m5 I tested is back up and 5 of 6 C6 stringers work. The only one I could not bring back was a full dead string of c6. when I blast it, it will light up but won't stay lit after the fact.

SO, this is just a beginning test and like I said may have been done before. Also, I have no idea what it did to the stringers/bulbs to make them work again nor do I know how long they will last for. What I do know so far is that they did not all light up before and now they do. Just something for thought and comments. I'd love to hear what you guys think about this "fix".

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I have tested more and it fixed those too, except that one string that had a full string failure. I cannot get it to work at all. I was wrong on the model number of my tester. I took the number off CDB's current website, but the one I have is SF-102. It looks identical to the current one they are selling though. I made a small video and uploading it to youtube now if you want to see it. Once it's up I'll post a link so you can see what it did. My next step it to create a looping track in LOR and run these with a fade/twinkle/shimmer/step sequence for several hours to see if this is just a 10 minute fix or if it could possibly last somewhat long term. Still absolutely no idea what it did to them, but not complaining if they will work again long term :)

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Well, color me dumb. This is a great find, and something I should have tried 5 years ago! I zapped 2 failed strings that were in the bag to go to the recycler, and BOOM, alive they came. I hope someone who understands this chimes in to explain possibly why this is the case.

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Would you guys mind doing a burn-in on your repaired strings? Just plug them in, maybe indoors at room temperature and let them run at full on. Better yet, use a controller to blink on and off.

Diodes are funny things. There are rectifying diodes in the "blobs" and the LEDs are themselves diodes. An overstress may induce latent damage that would weaken the junction and may reduce its life. I realize you fixed these, but am wondering how long they'll remain fixed.

As for what happened inside when they got fixed, I have no answer yet.

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HHmm, after viewing the video, I was reminded of how we used to fix shorts on a printed circuit board. These are notoriously hard to find, so we would just crank up the voltage and current and wait for it to burn through the short. It wouldn't always work...

I wonder if these malfunctions are related to partial shorts, possibly by tin whiskers, and the overstress from the tester burns through them?

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I went back to those 2 strings. One is working and is plugged in to see how long it will stay on. Nothing to lose on it anyway.

The other one had problems, like a wire was fractured. It would lite if I shook the string, but not if I left it alone.

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It is Possible that the High voltage pulse is fixing poor connections in the string by "Welding" them back together. The proof

is in the testing. Put some of those on a Controller and start hammering it. This is very interesting, and now I am thinking

of getting one of those buzz boxes !

Tim

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I made a fairly intensive one minute loop on LOR with fade up from zero to 100, fade down 100 to zero, twinkle, shimmer, and on/off cycles at 100%. I hooked up 2 of the M5's, 2 C6 and the 5 bulb c9 retro stringer I had. Within the first 4 minutes, half of the green c6 string got that near failure twinkle to it and half the red c6 went out. I hit them with the tester again and they made it another hour without anything happening (I only had it on for about an hour). The M5 strings were great until about 45 minutes in. At that point, 1/2 of one of the strings went out. another blast with the tester and it was fine. The other M5 and all the C9's made it for an hour with this one minute loop with no problems. After the initial problem with the c6, they made it the rest of the time with no issue. SO, it's half and half with the results. I'm going to do more testing over longer times to see if they can take it long term. right now the most promising are the c9's and the one string of m5....

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I guarantee there is no long term life in any of those LED's.

In 2007 working for a major resort and convention center, they bought several thousand strings of LED lights, Most of these went on massive wire framed Christmas Trees. When light strings had problems, and unknown to me, they used the buzz boxes like you are showing and yes sometimes the string would light up, but they did more damage than good overall.

How do I know? I have a large number of those LED strings, every year from 2008 to today the failure rate is very high. It took me 1 week last year just to repair all the failures of these Buzzed boxed LED strings, this year I have had only 2 of these strings to fail. The buzz box may look like it fixes it now, but the LED's are now called the "walking wounded" and will fail later.

Yes I know how to test and repair LED light strings safely and the buzz box is not the way.

Please be careful with your LED lights, you have your display counting on them working.

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Dennis, could it be that the buzzed strings were already faulty (why they were buzzed presumably) and that the failure rate is simply a repeat occurrence of the original failure?

If after the repair, all of the lights are working, it does point towards an open in the circuit that was closed by the high voltage pulse.

As for damaging the diodes, note that ESD diodes in CPU's are small diodes (strings of two or three actually) connected to each pad (part of the lithography) and designed to withstand thousands of volts. These diodes are extremely small when you compare their cross-sectional area to the area and current rating for normal LED's. So, I wouldn't expect a static-like discharge to have any effect on the string.

But that's just my theory.

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Yes I know how to test and repair LED light strings safely and the buzz box is not the way.

Please be careful with your LED lights, you have your display counting on them working.

Dennis,

Any tips/advise on fixing LEDs the right way that you can share?

Thanks in advance,

Glenn

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Gotcha Dennis. I figured if I got any extra life out of them, it would only be on things easy for me to replace, and, they were going in the recycle pile anyway. Time will tell if I want to use them.

I'm with Glenn, if you would share with us some of the methods you use, that would be awesome.

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Just as a heads up, out of the failed strings this year I actually had one come back to life after I had it back in the house. The real test is in the cold outdoors under stress. Some of these strings might actually fail from the cold and start to work again when they are warmed up inside.

Just chiming in with my 2 cents

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It is very true that temperature could affect the failure rate of a set of LED's. As some sets may have components that are Temperature sensitive. For example, there is this chime box that is required to install aftermarket stereos in 2003 Cavaliers, this box fails to work went it is below 32 degrees outside, for some unknown reason the components inside it are temperature sensitive, when they should not be, some LED strings could possibly be the same way.

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I'm going to throw out an idea for LED repair and let people run with it who have the inclination to make it actually work.

At one point I bought a bunch of CREE high powered (1W) LEDs. I noticed that even without enabling the output on my switching benchtop power supply that the LED would glow faintly when one lead was attached to the power supply. I expect what was happening was the power supply was generating a very-low current, but high enough voltage in the MHz frequencies (basically a small radio transmitter), that the LED was dissipating the current to air and was sensitive enough to glow even with this little current.

So, maybe with a little more transmitting power, you could energize a string enough to glow and find the break.

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