LedTrix - One "Unlit" LED lights a complete Column - ??"How / Why"??

T.D.Sutton

T.D.Sutton

New member
LedTrix - One "Unlit" LED lights a complete Column - ??"How / Why"??

I know it is "Old School" but my two panel "Original" LedTrix panles are integral to our display for disseminating information ie:- Tune to, traffic hazzards, etc, etc. One panel has intermittently displayed a lit or partially lit column or two during the show's run, taking it down from 16 feet above ground to change a LED is a little difficult while the show is running, it has to be the next day, and we are not getting any younger !!

Question ?? how can one "unlit" LED actually light a complete column, it doesn't seem possible, what has "failed" or gone "Bad" in the LED as they appear to operate fine as LED's after removal!

Sooo.. ?? can anyone with a better understanding of the mechanism involved in the matrix operation of the LedTrix describe to this "Old Guy" where/what to look for, what is actually creating the problem! I cannot figure out the reason, just replacing an unlit LED usually "fixes" the problem until next time, but why ?? :-( On more than one occasion the same LED position has failed, which seems very odd to me.

Any observations will be gratefully accepted :)

Terry
 
Re: LedTrix - One "Unlit" LED lights a complete Column - ??"How / Why"??

Why they go bad - not sure - but I believe what happens is that there is leakage current going through it that messes up the multiplexing setup used on the Trix so instead of blocking current in the one direction, it allows it to flow to the other column lines and turns them on (partially). I have replaced several in the past as well...

I still have my 2x2 setup stuck in the corner of my garage - haven't used it in years...
 
Re: LedTrix - One "Unlit" LED lights a complete Column - ??"How / Why"??

budude said:
Why they go bad - not sure - but I believe what happens is that there is leakage current going through it that messes up the multiplexing setup used on the Trix so instead of blocking current in the one direction, it allows it to flow to the other column lines and turns them on (partially). I have replaced several in the past as well...

I still have my 2x2 setup stuck in the corner of my garage - haven't used it in years...
Click to expand...

Thanks Brian, what you have described is what I understood to be the case, being of a curious nature I pondered if there was something that one could "look at or measure" in a LED to determine if it was "Bad" prior to installation. I have since gathered that as I am using a Pic C interface that device sends out blank frames continuously when there is no data input. This means that the multiplexing of the rows/columns is running continuously with activity on the Buss lines which could provide the mechanism for a column to light if an LED had gone "Bad" as you described, although my brain cannot see how :-(

Maybe the "problem" with the occasional dud LED is due to our sourcing "cheap" bulk pack LEDs to use in our home-built LedTrix panels rather than buying "known good or better quality" LED's in the first place, although it doesn't answer my question :)

Since replacing a couple of LED's in the one "faulty" panel I ran it continuously with a loop of text files for two day's and nights, soaked ran it with no data for a day, then re-ran the test loop for yet another day with no further problems showing up. Hopefully it will happily now run for the 5 weeks of our show :)

Head scratching to be continued while pondering the "problem"

Terry

PS, it is a shame your 2 x 2 is sitting idle :-(
 
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