Daisychained TLC5940 - chip 3 doing strange (modified text)

Other Hardware LEDs and Multiplexing
1

OK, so I have a little issue anyway.

It's nothing big, but I can't figure out what happened.

I had a perfect setup on my breadboard, transferred it to a protoboard for permanent use, and now I have 2 LED's flickering.
There are three TLC5940's daisychained, with 12 RGB LED's attached to them.
This means that there is one lead of LED 11 on the third chip and LED 12 is connected to chip three completely.
The one lead (blue cathode) and LED 12 are flickering.
When, in my program I give the command to have all the red leads light up, the blue lead and the green and blue leads connected to chip three flicker.
I already replaced the chip, checked the connections, there are no shorts anywhere.
However, when I have my program running I can hear short beeps coming form my multimeter when I place it on any of two the LED pins of chip three. So, it seems there is a connection somewhere, but I can't trace it back.

Before I go disassembling my whole board (so many wires, it's hard to reach in with a soldering iron), I was wondering if anybody had any idea on what this could be, and how to solve it.

Any help would be great :slight_smile:

2

Updated, since the problem changed.

3

You do have decoupling on every TLC5940 don't you? 0.1uF per chip and at least 10uF on the board somewhere? Switching LEDs is fast high current switching and decoupling cannot be skimped on.

4

I have decoupling on all three TLC chips yes, 0.1uF.
Not the 10uF on the board, I could add one to the power supply lines, but I had the exact same setup on a breadboard which worked without any problem.
It is only the third chip that isn't working as it's supposed to, and the chip itself is OK, so are the LED's.

5

Problem fixed, I resoldered all connections because the resistance wasn't OK, now it's working as expected.
Just, when I have all colors lit up it has a little flicker, but that is no problem since that won't really happen, and it only occurs on one or two LED's at the time.