# LED flickering -- what to do?



## jeffkrol (Jun 5, 2013)

Depending on the power supply, the diodes are 3 or 4 in series. Point is it looks like a whole row is failing.
There is the trace supplying power, 3 or 4 diodes, and a smd resistor. Problem is which one is failing..


----------



## mikeh (Jan 13, 2016)

jeffkrol said:


> Depending on the power supply, the diodes are 3 or 4 in series. Point is it looks like a whole row is failing.
> There is the trace supplying power, 3 or 4 diodes, and a smd resistor. Problem is which one is failing..


I may be misunderstanding you (or the wiring you're describing) but I think my video misled slightly. That is just showing one little area of the light. There are 3 rows of 10 leds, and the last 3 out of a row of 10 are the ones failing. 

Now, assuming it isn't just that my vid didn't show the whole row, are those three probably still isolated as I think you're describing? If so, then it does make sense that they'd be failing together, and even blinking in unison (which I hadn't even thought much about until now). You're right though, figuring out which is failing will be tough.


----------



## Nlewis (Dec 1, 2015)

I had a Marineland fixture do this before due to condensation getting into it. I was able to take it apart and solder in a jumper over to another led row and it worked.


----------



## jeffkrol (Jun 5, 2013)

mikeh said:


> I may be misunderstanding you (or the wiring you're describing) but I think my video misled slightly. That is just showing one little area of the light. There are 3 rows of 10 leds, and the last 3 out of a row of 10 are the ones failing.
> 
> Now, assuming it isn't just that my vid didn't show the whole row, are those three probably still isolated as I think you're describing? If so, then it does make sense that they'd be failing together, and even blinking in unison (which I hadn't even thought much about until now). You're right though, figuring out which is failing will be tough.


The whle board is composed of 3 led in series. Each series row is in parallel. 
Like this:









Biggest problem is I believe those are all surface mounted and the resistor on a row of 3 can sort of be anywhere.
Also can you get to where the diodes are connected.. Where they are attached to the board...
If you can there is a sort of way to test each w/ a VOM though an intermittent fault would still be hard to find..
Best to wait till it fails completely..
There is no easy way to repair it. Well there is but not for us mere mortals..
to destructively eliminate the problem one just needs to break the row connection by either cutting the trace or destroying a diode..

good thing, sort of, is you only lose 3 diodes..

Is the power supply 12V BTW???


----------



## mikeh (Jan 13, 2016)

jeffkrol said:


> The whle board is composed of 3 led in series. Each series row is in parallel.
> Like this:
> 
> 
> ...


OK, that diagram shows what I thought you were saying. Thing is, it must not be physically laid out like it is electrically, because you're saying I'm losing one of those whole branches, right?
My layout would look like this: O's as on, x's the ones failing.
O O O O O O O O O O 
O O O O O O O O O O
O O O O O O O x x x

And it is a 21v transformer, not 12v.


----------



## jeffkrol (Jun 5, 2013)

Yes..
21V????? Doesn't make sense.


----------



## mikeh (Jan 13, 2016)

So I've lost (intermittently) another group of three. And a correction to my earlier description, there are actually 39 leds in a 13 x 9 configuration.
I can get to where the diodes are connected--all I have to do is remove the splash sheild. It looks like they are just soldered right there out in the open. I can see everything without even removing the plexi. I can see the resistors too, and so have some suspicion of which are associated with each of the two groups of three. Are they likely to be bad, or just be badly soldered somewhere?

m


----------



## jeffkrol (Jun 5, 2013)

Hard to say.. You could bypass the resistor w/ a jumper wire if you suspect that is the problem.. 
also a lot of times the resistors are not at the "end" of a triple.. Electrically they can be put anywhere within the 3.. diode resistor diode diode is the same as diode diode diode resisor. 
Just briefly because the amps will be larger. but still in the diodes range..usually..
The resistor actually drops the voltage from the ps slightly to the string of 3.. along w/ being a sort of "governor" for amp draw. 

NOTE: watch your eyes, these things can do damage ...

If it is a diode (you can do the same jumper thing but voltage will be huge (for them) across the remaining 2 diodes...
Like the voltage across 3 after resistor is like 9-11V/3 = 3 to 3.6V 
At 2 diodes.. it would be 4.5 to 5.5v each.. At that voltage they will draw dangerous (for them) currents..

I suppose one could build a jumper wire w/ a resistor as a test probe..
Problem is if it is a diode now what??? 
Guess somewhat the same w a resistor..

As to a bad trace (or say corroded) finding that is also problematic..

W a VOM and access to the plus minus pads.. each can be tested seperately easily.. Diode will dimly light w/ a VOM set to ohms or diode..
VOM will tell you if all resistors are in range..
Testing LEDs with a Multimeter - All


> I will admit that I have done this test without a resistor and have had no problems. This meter only outputs 3VDC on the diode scale, my fluke outputs 8VDC.


1/2 doz cheap VOM's and none is over 3V


----------

