Only first few LEDs are working

Issues
1

Hello,
I installed a 5m strip of Sk6812 on the back of my tv a few months ago and has been working flawlessly with no level shifter until a few weeks ago. Only the first 6 LEDs are responding, I asked in the discord and some people suggested using a level shifter and I got sn74ahct125n and wired it as so (except I am using a D1 mini with D4 as my pin

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But this didn’t solve the issue.
Then I tried hooking up a new D1 mini to the strips so I flashed and connected the LEDs to a new module with no difference.
I do want to note that when this issue started to arise the LEDs will just freeze up except for the first few and touching the malfunctioning made it work until it happened again (not that often). Then a little while after it would freeze up but touching the malfunctioning LED will only change the colour so the effects didn’t work at all, so I asked on discord. When I installed the Level shifter I tried touching the malfunctioning LED but nothing would happen to the malfunctioning LED.
Is my strip already dead or are there other things I can try like somehow testing which pixels are dead or replacing/jumping pixels?

2

Try jumpering the data line over LED 6 and 7. It’s possible one of them went bad.

1 Like
3

Is output enable active high or active low? Thought it was active high meaning don’t tie to gnd

4

I thought the same but I just followed the schematic

1 Like
5

Here is corrected diagram
corrected

1 Like
6

So if one pixel is dead, the rest of the strip don’t light up?

7

Possibly. If one of the leds has gone bad, it might not pass the data signal through it. Just something to try.

8

I may try to set oe to vcc. See if life changes.

9

If one pixel is dead and pixel in the beginning of the strip then entire strip is not responding. If you remove bad pixel there is a chance rest of the strip will be saved.

10

@Aaliankhan – In case you missed it, @srg74 's corrected schematic ensured the level shifter would have stable output via the following changes to the SN74AHCT125N:

  1. Unused inputs (2A, 3A, 4A) are connected to ground.
  2. Enables (2OE, 3OE, 4OE) are connected to ground.

This is necessary. The datasheet at page 3, has the following critical note:

All unused inputs of the device must be held at Vcc or GND to ensure proper device operation.

By leaving those floating (as you did initially), there could be no guarantee of proper operation of the chip. Maybe 1A and 1Y would work correctly because of grounded 1OE, or maybe the other three being left floating would cause weird interactions internally in the chip and mess with your output signal. Better to do as Srg74 says. :slight_smile:

11

Sounds like a bad led. We use the individual leds on pcbs at work and if one goes bad then all following leds fail to work or do strange things.
As suggested above short the data in and data out of the first bad led will confirm this.

12

Hello, thanks for all the suggestions, today I found some time to work on this, as suggested I have grounded the pins on the level shifter, that didn’t make the LEDs light up.
Next I added a jumper. I added a jumper right next to the working led and then proceeded to put the other side of the wire to the non-working. After soldering and powering it back on nothing changed so I tried moving the second wire further along the strip, but that didn’t change it much either.
I’m pretty much stumped at this point, any recommendations will be appreciated otherwise I will be buying a new strip

Here is an image of my jumper

13

Are you sure you connected correctly your data wire to your strip? Arrows on strip should show away from your controller.

14

yup, I checked and the arrow is pointing away from the microcontroller

15

Couple of issues,

  1. Your guess is the output of the last lit LED is bad or possibly “corrupted” by the input of the 1st unlit LED
    Either way, if you move back one LED to the 2nd last good output you’ll be able to see the effect of your jumper a little better. If doing this lights ONLY one new LED you probably have a software not a hardware issue.

  2. You can (reasonably) safely tie two inputs to one output - that’s what I 'm suggesting by moving your jumper back one LED.
    But you shouldn’t tie two outputs together, which will happen if you don’t cut the data trace from the LED that’s just before your jumper endpoint.

You’re trying to jumper the data lines around a string of potentially bad LED’s, but you have to disconnect the lines you’re assuming are bad.