Rainbowcube - one LED gives wrong colors. HELP?

Products & Technology Arduino & Seeeduino
#1

There is exactly one LED that does not light up correctly in the Rainbowcube I just finished building. I specify 0xffffff as the color for all LEDs. I expect this to be white. It is, for all LEDs except for one, and that one glows green.

  1. I checked this LED’s elements, one at a time, with test leads, to make sure it is not the LED itself that is defective; they each light up the correct color.
  2. I substituted the 8x8 matrix for the Rainbow Cube. All bulbs glow white, as they should. This means the problem is not in the Rainbowduino.

The only thing that is left is one of MANY solder joints in the cube, or a faulty component on the panel (base PCB). None of the components on the panel is especially heat sensitive, except maybe the voltage regulator, but the cube is being powered by the RainbowDuino, so I don’t think the VR is being used. I have examined the joints carefully, resoldered some just in case, but don’t see any problems there either.

It almost has to be a solder joint. With multiplexing, if any one joint was failing, I would expect to see more than one LED lighting up wrong, and that isn’t happening.

PLEASE, if you have any ideas on how to track this down and fix it, let me know! I’m at a loss.

thanks in advance!

#2

I still need help. I was hoping that Yuriq might answer here!

Here is what I know for sure:

Under software control, all LEDs work properly, except for one which can light up with green (with variable intensity) but not red or blue. For that one LED, the LED itself and solder joints work when I apply power through a current-limiting resistor to the solder joints.

#3

Good debugging work so far.
The problem has to be with the solder joint or traces going directly to the R and B ground pins for that LED.
If the problem were anywhere else I would expect to see an entire row malfunction due the the LEDs being wired in series.

Try to trace continuity to its neighbor LED and see where the connection is broken. Start by finding where the Green (working) pin has continuity, you should expect the R and B pins to have continuity there too.