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Assistance required to find a short in a simple electronic board

Discussion in 'Power Electronics' started by fxdls110, Aug 24, 2021.

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  1. fxdls110


    Aug 24, 2021
    20210824_103822-min-min.jpg 20210824_103845-min-min.jpg Hello, everyone.
    First off, I will state that while I have reasonably decent soldering skills, know my way around a multimeter, and can identify most simple components, such as resistors, capacitors, diodes and transistors, my diagnostic ability leaves a lot to be desired.

    What I have is an aftermarket, integrated tail light assembly for a Harley Davidson. This has the tail light, brake light, left and right turn signals all in one, small package.
    A friend of mine and I were on the road when we were hit with some of the worst torrential downpour weve ever ridden in.
    Long story short, the light assembly got a bit wet within the housing. Now, all of the individual lights DO work, however, the lights that are supposed to be on for the "tail light" function do not come on, and only come on during the "brake light" function, which is when the same lights just become brighter when the brake switch is applied, if that makes sense.
    I have cleaned all of the water marks off of the board as best as I can, and cannot seem to find the source of the interruption of power that is preventing the tail lights from coming on, so I am wondering if someone who is much more proficient could perhaps point me where to look.
    Last edited: Aug 24, 2021
  2. Bluejets


    Oct 5, 2014
    If you have a Harley Davidson, I'd suggest you could afford a new one.
  3. Externet


    Aug 24, 2009
    What does "a short" mean to you ?
    Scrub the board with alcohol and brush; dry in front of a fan a few hours and retry.
    Kabelsalat likes this.
  4. fxdls110


    Aug 24, 2021
    Ha, while I do take very good care of them, my bikes are much older, twenty years old even. Not everyone wants to spend the money on brand new junk. I believe it to be a waste, even. Im not a credit card biker, Im afraid. Its not really about the money, I just dislike wasting things, and I just wanted to see if it could be fixed and perhaps learn a thing or two while Im at it. The thing has a lifetime warranty on it, and the company has already sent me a replacement and acknowledged that the board needed to be sealed to prevent this from happening.
  5. dave9


    Mar 5, 2017
    Determine which wire is used to energize the tail light, and then you trace the circuit, more of a pain since they decided to use a black pcb. Since there is an IC in the top right portion of the pic, I'd also get the markings off it and then the datasheet to see the pinout and functionality, to proceed further tracing where power stops... and then there is that (transistor?) right next to it, again get markings, determine what it is, and that may be the fault if the water caused a conductive short, especially if the factory was sloppy with not getting all the water soluble flux off so it was completely intolerant of water, plus they really should have used some mask over LEDs and conformal coating, is pretty inexcusable for a tail light to not be built to higher standards where a mere leak causes loss of functionality for something this important.
    fxdls110 likes this.
  6. fxdls110


    Aug 24, 2021
    Thanks a lot. I will look into this when I get the chance- probably tomorrow after work. I did scrub it with a toothbrush and a bit of alcohol a few days ago, which removed the "deposits" left from the water after the water had dried. I already know it is the blue wire (appears green in the photo) that supplies the tail light function with power, though it is indeed difficult to see where the traces lead, due to the board being black. Interestingly, the row of lights shown in the bottom picture, on the top, center portion of the board, are the license plate lights, which are also supplied by the blue wire, though these work fine, leaving the opportunity to perhaps do a bypass for testing.
    My diagnostic skills just arent very well versed, but I have desoldered EPROM chips from ECM units, and soldered sockets in their place so that the chips could be removed, reprogrammed and replaced, and Ive also replaced some capacitors and removed surface mount LEDs in order to solder in lights of a different color in motorcycle gauge pods and such.
    If you ever need a guy to build a good PC, or high performance engine or transmission, or an entire car or motorcycle from the ground up, or a draftsman or CNC operator, Im your guy, but just dont ask me to find the problem with a board like this one haha.
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