Led Help

[dizzy_chicken]

Ok i just made this led matrix with every 4th led connect in series and then goes to a control board. Ive tested each led and they all work. Now when i supply it with 12v most of the groups light up.

Now heres the weird thing. I go in and test the group of 4 leds that dont light up, with 12v but they wont work. Then i test the sequence from 1st to last each led 1 at a time and they all work. I then tested them 1st-2nd, then 1st-2nd-3rd and when i get to the last one it doesnt work. I do the same in reverse (4th-3rd, 4th-3rd-2nd) but when i do all 4 together they dont light up?

Anyone know why this is? All the leds came from the same batch and are individually tested and check for correct polarity when i put them in to avoid any of these problems.

[pebe]

Your description doessn't make much sense. Can you draw a circuit of the matrix and the controller?

[dizzy_chicken]

Ok umm.. forget the matrix and the controller for now. I have a 4 leds in series (3v each) and i supply them with 12v. They do not light up.

I test each one with 3v and they work. I then test them as series 1-2, 1-2-3 will work, but when i test all 4 together they will not light up. I do the same test in reverse order so the last 3 will light up but when i connect the 4th the same thing happens.

I have other groups for 4 leds that light up and all came from the same batch. So when i connect power to my led matrix i get groups of "dead pixles".

Sorry i dont have a diagram i can show you. But the matrix is simple enough and was made by connecting 4 leds in series to form a group. Then every group is then soldered in parallel to a 12v source with sufficient current.

[pebe]

It seems that either the LEDs have a forward voltage drop greater than 3V, or else your 12V is less than 12V.