Problem with interactive LED display–one quadrant doesn’t light up

[davidplotz]

My son and I are building a 4 panel interactive LED display. We just completed the first board. One entire quadrant (quadrant 3) doesn’t light up at all, though the others work perfectly. Any tips or advice? All the solder joints look OK. 

Thanks

[davidplotz]

Addendum to my previous note. None of the LEDs respond to movement in the light or the dark, but most of the LEDs in the dead quadrant do have a dim glow. 5 of the LEDs in the quadrant (in a W shape) do not have any glow. Thanks, and I appreciate the help. 

[Windell Oskay]

There may be more than one independent issue; the lack of response *may* not be related to to the five not lighting up.  

The first step is to check the 5 LEDs that are not lighting up to see what the issue is.  Check to see, for example, if any of the LEDs is backwards by looking for the flat sides of the collars.  Check to see if any of those LEDs is not properly soldered.  If that all looks fine, then one of the LEDs may have been damaged.  Use a fresh LED, and place its two pins across the pins of each of those 5 LED locations, to see if it will light up a little bit.  

Please let me know what you find, and I’ll try to help you out from there. :)

[davidplotz]

I’ve now completed all four boards. I also have a quadrant that is very dim. The lights all work, but they are not bright like the other LEDs. Any thoughts on that? 

Again, thanks from a novice. 

[davidplotz]

Hi Windell

Thanks

RE: The first step is to check the 5 LEDs that are not lighting up to see what the issue is.  Check to see, for example, if any of the LEDs is backwards by looking for the flat sides of the collars.  Check to see if any of those LEDs is not properly soldered.  If that all looks fine, then one of the LEDs may have been damaged.  Use a fresh LED, and place its two pins across the pins of each of those 5 LED locations, to see if it will light up a little bit.  

I tested the five dead LEDS in the dead quadrant, and four of them lit up an LED that I held across the pins. But I was not able to get the fifth to light up at all. (The fifth also looks like it is the last one in the series). 

I then swapped out that fifth dead LED with a new one, and it is still dead (as are the other four.) Suggestions?

[Windell Oskay]

On the dim quadrant: Double check all of your resistor values in that quadrant.

On the mystery quadrant: that is a surprising result.

The ten LEDs in that half-quadrant are connected in series.

So, if one LED were damaged such that it gave no connection (or it was in backwards), I would expect all five to light up when you connect an extra LED across the pins of that one location. You would not be able to light an LED at any of the other locations.

And on the other hand, if one LED had a short circuit (for example, if its two pins were soldered together), I would expect the other four to normally be lit up, but brighter than usual.

Do you still have the same behavior now that you’ve replaced that LED– as in, will the other four locations still light up an LED? And, do you have access to a multimeter?

[davidplotz]

Thanks Windell. I hugely appreciate the intervention. I will go deeper into this over the weekend, but a few quick answers

I replaced the one LED and still have the same situation with the dead ones, but I will reexamine it more closely on the weekend. 

I don’t have a multimeter.

I double and triple checked the resistors in the dim quadrant, and they all look good, unfortunately. Any other tips on that? 

[Windell Oskay]

Okay, please file me under “puzzled.”  I may be able to try and damage a panel here for comparison, to see if I can find any possible explanation.

One the dim quadrant: I suggest that you try *gently, with the power off* replacing the IC in that quadrant with a  different one, to see if that helps.

[davidplotz]

THanks.

 Last question before I surrender. I swapped the IC in the dim quadrant (100 quad)  and got this weird result: The whole board became non-responsive. Half the LEDs are lit up, but dully (including in a previously dead quadrant!). None of the LEDs now respond to movement. They just sit there. 

One point that may be germane. The first time I swapped the IC I put it in backwards and turned the board on. Then I realized I had put it in backward, and switched it. COuld that have messed up the board in that way? Is there some other obvious fix. Thanks, and this will be my last bothersome note. 

I appreciate your thoughts! 

D

[Windell Oskay]

No need to surrender.  It sounds like you have a damaged IC.  Turning one around backwards and applying power will definitely break it.  Do you have a replacement on hand?

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