Problem with led lights

[Clancaster23]

I have four sets of led's over my 180. They have two switches on each of them and there's three fans, one switch runs one fan and 20 leds and the other switch runs two fans and 20 led's. I was looking earlier cause the one on the end of the tank didn't look right so I looked under and saw that half the lights, the entire switch, wasn't lighting up. The fan comes on that's on that switch and I might get an occasional flicker from the lights but they don't come on steady. I took the light apart and switched the power around to see if it was that because the other half works fine but it wasn't that because it does the same thing on the other switch. Before I closed it up, I got them to come on steady but as soon as I got it over the tank again, they won't come on. I might get a flicker a couple times but won't stay on steady. I replaced maybe half the lights on the board with others I wanted in it. I'm wondering if one of the solder points became unattached and if one light is loose that the whole strip won't light up or what. I'm lost on this one. I don't think it's the actual parts inside because the other half works on both sides fine. Also, this entire part that's not working, all the leds are the UV color. Not sure that has anything to do with it or not.

[mcgyvr]

sounds like you have a shorted or loose wire/cold solder joint.

[rocsec1]

Second the loose wire. When you put it back together the wire got pushed out of place again

[Clancaster23]

I don't think it's a loose wire. I was able to take apart the light today and I was able to get it to turn on again but I turned it off and back on and once again, it wouldn't turn back on. What it sometimes does is even though they won't turn all the way on, sometimes when I hit the switch, I'll see a pulse go through them like they are getting juice but they just can't fire up all the way. So I looked to see what ones were not working at all and found one that was not doing anything. I took a closer look and it looks like the chip that is on this particular led is blown. It has a white spot in the middle of it and the ends of it are brown like they are burnt and you can see others next to it are fine. They all say "201" on them. Would it be possible to find this particular microchip and somehow solder it on or is the whole half of this light done?

[triggreef]

Still sounds like a bad solder to me.

[Clancaster23]

Please elaborate. A bad solder on this particular chip? This led is not one I replaced so it's still the original one. If you're saying it may be one of the ones I replaced, I did check them all and they seemed to be all firmly attached.

[dartier]

Based on the photo, I would agree that the SMT resistor looks like it has had its magic smoke let out. The LED beside it also looks a bit worse for wear as well, and may have contributed to the issue.

Do you have a meter with a diode test? If so you should test that LED and see if it is shorted or open. While you are there, test the resistor as well just to confirm it is dead.

A 201 SMT resistor is a 200 ohm resistor. You can likely find some on EBay or at an online electronic supplier. It will take a steady hand to unsolder and replace it though.

Dennis

[Clancaster23]

First, neither of the two of the LEDs on each side of the problem one is on the same circuit as it. Also, I noticed the discoloration of the other ones and that's just my crappy cell phone camera doing that. The other ones look fine, it's just this one that looks burnt and bad. And if you're referring to the bad solder job on the one on the right, this was my first time soldering anything so I know it's rough but I learned as I went.

As for testing, I do have a multimeter but I have no clue how I'd test this with it. This is my multimeter: http://i.walmartimages.com/i/p/00/04...00_500X500.jpg If you can maybe walk me through how to test each, I'd definitely be willing to do it and post results.

I'm glad this post found someone who knows this stuff, the help is appreciated.

[dartier]

Don't worry about your solder job. I would be the last person to criticise someone else's soldering. If you live in glass houses and all that ...

Ok, so first you should probably test the resistor. Set the dial of your meter to 2000 OHMs. You have a 200 setting, but depending on tolerances, your 200 ohm resistors may be just over that. If you go over the range of the meter on its current setting, it will usually show 0L.

Touch the positive (red) and negative (black) probes to each side of the the 3 resistors in your photo. Observe what the meter reads for the 3 resistors.

Now repeat the test, but touch the negative and positive probe top the opposite ends of each resistor. I am guessing that those resistors are in parallel the the LEDs and are intended to prevent the whole string from going out if 1 LED fails. By reversing the polarity of the test, you should be reverse biasing the companion LED, which will prevent it from affecting the reading.

Now you should have 6 readings collected. Compare the readings for the "good" resistors to the (suspected) "bad" one.

Those resistors may mess with a diode test, but we can still try. Set your meter to the diode test. It is immediately to the right of the 200 OHM setting based on the meter photo. Now test the 3 LEDs in your photo by touching the red to the positive and the black to the negative of each LED. The negative is marked with a "-" (based on your photo). Do the same test with the polarity reversed on the 3 LEDs. Note the results.

During the test, the LEDs may glow slightly if you have the polarity correct and if your meter is testing the voltage drop through the diode. This can be a handy way to determine the colour of a LED when you have a whole pile of them. During the diode test meter may also make a tone when the polarity is correct (which is very handy).

This should help us to determine if the resistor is bad, and if the LED is intact.

Dennis

[Clancaster23]

Ok well first off, thanks for the very good directions in helping me figure out what to set the multimeter to and how to do it. Now, I tested all three in the picture just as you said an I get 200 readings on all six tests. Even on the resistor that I claimed to look bad I get a 200 reading on and both ways meaning switching negative and positive probes. Actually the suspected one goes to 198 but I'm not sure that pegs it as being bad.

What I did do was since I knew how to test all the diodes, I tested all 40 of them and I did find one that is on that same circuit that won't light that reads around 005, both the light and the resistor read the same. Not sure if this tells you anything though.

Also, none of the LEDs did any glowing while I was testing them either although I did try that on a small strip of the plug in rapid LEDs I have and those did.

[dartier]

Originally Posted by Clancaster23

Ok well first off, thanks for the very good directions in helping me figure out what to set the multimeter to and how to do it. Now, I tested all three in the picture just as you said an I get 200 readings on all six tests. Even on the resistor that I claimed to look bad I get a 200 reading on and both ways meaning switching negative and positive probes. Actually the suspected one goes to 198 but I'm not sure that pegs it as being bad.

The 198 reading is within tolerance, so even though it looks rough, it is still functioning.

Originally Posted by Clancaster23

What I did do was since I knew how to test all the diodes, I tested all 40 of them and I did find one that is on that same circuit that won't light that reads around 005, both the light and the resistor read the same. Not sure if this tells you anything though.

What did the ones other than the bad non-lighting one read? The fact that the resistor is reading the same as the diode would point to the diode being failed closed. When you are testing the resistor and getting the same reading as the diode, this shows that the LED is shorted and you are really reading the resistance through the LED (005) opposed to the 200 that the resistor should show. To confrim that, make sure you test that resistor for resistance in both directions. A functioning LED will not pass reverse current which would allow you to see the resistance of the resistor (200).

Originally Posted by Clancaster23

Also, none of the LEDs did any glowing while I was testing them either although I did try that on a small strip of the plug in rapid LEDs I have and those did.

That is probably due to the resistor that is in parallel with the LED.

What are the symptoms again? None of te LEDs work in the light, or only the LEDs on 1 string fail to work and all the rest do?

If it is none, then it is either a bad switch, or a ground fault that is causing the power supply to trip a resetable fuse and shutdown.

If it is only 1 string that fails to light, then the issue is in that string. Testing the resistance of portions of the string should give you N x 200 ohms depending on how many LEDs are included in the portion you are testing. Again, reversing polarity should reverse bias the LEDs and allow you to get a reading of the resistors.

Dennis

[Clancaster23]

I just hooked the board up to the switch just to see what I'd get and the lights came on right away. I turned it off and on five of six times and they worked every time. I did it once more and it's back to it's flickering self. One time I left it on and as it was flickering, they suddenly came on steady and full. Turned it off again and just the flickering again. I took a video of what they do for the most part.

http://vid303.photobucket.com/albums...ps709e9126.mp4

And I don't know if this means anything but I noticed the one resistor and led that is suspect, that led is out but it still shows a reading of 200, both led and resistor. The one I mentioned in my previous post that reads 005 is also out. I'm thinking shouldn't I be getting a low reading on the suspected one if the led is out just like the one that really is out?

[Clancaster23]

All diodes and resistors read 200 except for the one that read 005. Both resistor and diode read 005.

The symptom is on this string (20 LEDs) all are not turning on. If you watched the video you'll see that the most I get is a flickering of the light. Sometimes they will come on full power but it's only on a rare occasion.

These lights have two different plugs, one for each string of LEDs. The second string works fine. If I put this non-working string and plug the board into the other strings plug I get the same effect so the problem I'm thinking is somewhere along the board. I have maybe one or two LEDs out on other light fixtures that are the exact same as this ( I have four of these over my 180) and I don't have this problem with them.

[dartier]

Originally Posted by Clancaster23

I just hooked the board up to the switch just to see what I'd get and the lights came on right away. I turned it off and on five of six times and they worked every time. I did it once more and it's back to it's flickering self. One time I left it on and as it was flickering, they suddenly came on steady and full. Turned it off again and just the flickering again. I took a video of what they do for the most part.

http://vid303.photobucket.com/albums...ps709e9126.mp4

And I don't know if this means anything but I noticed the one resistor and led that is suspect, that led is out but it still shows a reading of 200, both led and resistor. The one I mentioned in my previous post that reads 005 is also out. I'm thinking shouldn't I be getting a low reading on the suspected one if the led is out just like the one that really is out?

The flickering sounds like either a cold solder joint in one of the LEDs that you changed, or perhaps a solder bridge to ground that is not 100% shorted but very close.

Two things you can try.

1. Get a magnifying glass and look at each solder connection looking for a bad joint, or a bridge to a ground plane.
2. With the light on apply gentle pressure to each LED in the string to see if you can cause it to stay on. IF any LED (with pressure applied) causes the string to light, and stay lit, you have found one that requires a closer look.

For the 2 failed LEDs, you have 2 failure modes present, the first failed as a dead short, so you see only the resistance of the shorted LED (5 ohms) and not the resistor. The other failed open, so you get 200 ohms, the resistance of the parallel resistor.

Originally Posted by Clancaster23

All diodes and resistors read 200 except for the one that read 005. Both resistor and diode read 005.

The symptom is on this string (20 LEDs) all are not turning on. If you watched the video you'll see that the most I get is a flickering of the light. Sometimes they will come on full power but it's only on a rare occasion.

These lights have two different plugs, one for each string of LEDs. The second string works fine. If I put this non-working string and plug the board into the other strings plug I get the same effect so the problem I'm thinking is somewhere along the board. I have maybe one or two LEDs out on other light fixtures that are the exact same as this ( I have four of these over my 180) and I don't have this problem with them.

With the light off and disconnected, measure the resistance between the negative terminals of each of the LEDs and the negative (white) feed wire for the string. The first LED from the negative will be 0 ohms (direct connection), and each LED along the string should increase in resistance when measured against the negative terminal wire. If any read 0 ohms, other than the first in the string, then you have found a short to ground. You have 2 white feed wires (1 for each string), so try them both until you find the one that is for the problem string.

If you find any that appear to be a short to ground, examine the LEDs terminals looking for a solder bridge. It is not uncommon to damage the solder resist mask when you rework boards, so you may have inadvertently exposed the ground plane and have a solder bridge that is almost touching. Thermal expansion could explain the flickering in this case.

Dennis

[Clancaster23]

Ok, I measured the resistance of the negative terminals with the white wire of the faulty string and found zeros. I can see how the string goes since the string is sort of raised and you can see the path it goes throughout the board. Here's what I got from all 20 LEDs on that string:

1 - 0
2 - 200
3 - 400
4 - 600
5 - 800
6 - 1000
7 - 1200
8 - 1200
9 - 1400
10 - 1600
11 - 1800
12 - 2000
13 - 0 <-----This is the one with the potentially blown resistor
14 - 0
15 - 0
16 - 0
17 - 0
18 - 0
19 - 0
20 - 0

I'm guessing that might mean something since they start reading 0 right at the problem one. Also, the one next in line, the negative solder doesn't look good but I wonder If that has any effect on the previous one? I attached a pic of both of them. The upper left one is the one that looks bad, the bottom right is the one with the possible bad resistor. That bad solder one looks even worse in the pic.



So if this one with the excess solder is the problem, can it be fixed?

[dartier]

Based on the photo, the traces look pretty wide with the LEDs and resistors in parallel. It all depends if it is single layer or multilayer board, with a ground plane under the trace. The LED has to be thermally contacted to a pad under it to cool it. So the odds are that there is the possibility of accidentally grounding a terminal if the solder blob is big and the resist layer has melted.

When you measured, did you use a higher setting on your meter? If you had it set to 2000 ohms, it would register an out of range condition. Try the next setting up (20K).

If it turns out to be a solder bridge. reducing the solder will usually fix it. Solder tends to bead on metal objects, so removing solder will usually disconnect bridges. Too early to say if that is what it is though.

If you could repeat the test on the higher range and lets see where that leaves us.

Dennis

[Clancaster23]

I actually just put it back over the tank since I have been redoing how I have all of the lights sitting over the tank and turned it back on. The whole thing including the problem string is on. I'm figuring it's only temporary until tomorrow when they turn on again. I'll know when I get home after work. I'll take it off again tomorrow evening and test at a higher level and post results.

[dartier]

Ok, I will watch for the results.

Dennis