LPD8806: One segment only outputs 2.7V
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LPD8806: One segment only outputs 2.7V

by niko001 on Sat Mar 23, 2013 10:18 am

Hi,

I've cut up a LPD8806-strip into 6 segments (with 4 LEDs each) and connected all Outputs to the respective following Inputs. This works fine for the first 3 segments, but the last 3 segments are much dimmer. When testing the output of the third strip with a multimeter, it only supplies 2.7V instead of 5V to the next strip-segment. I've tested all solder joints with a continuity tester, and they are fine. Before cutting up the strip, all LEDs were working fine (with the same 5V, 2A power supply). I've correctly adjusted the number of LEDs (strip-length) in the Arduino code. I've checked for solder balls and left-over wires and lightly pressed on adjoining ICs as recommended in the Adafruit Troubleshooting-Wiki. Does anyone have an idea what could be going on here?

Thanks!
Nick

P.S.: It doesn't look as "bad" as it is in reality on the attached pic. When running the strandtest-sample, the bottom 3 segments flicker or don't turn on at all, so it's not simply a brightness-issue.
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Re: LPD8806: One segment only outputs 2.7V

by pburgess on Sat Mar 23, 2013 11:35 am

Hi Nick,

Start by replacing the wires between segments 3 and 4. Though it passes a continuity test, this doesn't indicate how robust the connection is, and the solder looks a little "ball-y" there.

28 ga. ribbon cable wire seems like it might be a bit thin for that amount of current...but that would likely manifest as a gradual fading from segment to segment and not an abrupt dropoff as seen, so I couldn't say for certain. If the first suggestion doesn't work, I'd try moving the +5V and ground connections from the head of the strip to the middle (either the output of segment 3 or input of segment 4) so the ribbon cable is only carrying half as much current in either direction. (The strips don't care which end they receive power from, and clock & data would still go into the start of segment 1.)
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Re: LPD8806: One segment only outputs 2.7V

by niko001 on Sat Mar 23, 2013 12:35 pm

Hi pburgess,

thank you for your reply. You were 100% spot-on, the solder joint of the 5V-line on the 3rd strip was bad. The idea to move the 5V and GND-connections from segment to segment was awesome, that's how I found the bad joint.

Thanks again and have a good weekend,
Nick
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