PWM Dead?

Discussion in 'The Projects Forum' started by ArgusP4, Apr 18, 2015.

  1. ArgusP4

    Thread Starter New Member

    Apr 18, 2015
    5
    1
    Hey,
    I have an old motorized golf bag tote thing that I would like to get running. Motor tests good; Unfortunately it seems as though the speed controller is rather lifeless. How would I go about testing to see what's salvageable? I've built a few circuits so I have a vague idea of what all the components are doing, but don't know enough to reverse engineer this board. Any help is appreciated,
    Thanks,
    Argus IMAG0661.jpg IMAG0662.jpg IMAG0676.jpg IMAG0669.jpg
     
  2. ArgusP4

    Thread Starter New Member

    Apr 18, 2015
    5
    1
    Side note, I am 99% sure there is a battery meter mixed in the circuit (due to the lights) and I'm curious how that plays with everything else, but if that takes you too far off topic don't worry about it.

    Argus
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,974
    744
    should be easy to reverse engineer, as the 14pin chip is a dual 555 timer (ne556), its a matter of finding out which pin drives the motor and which transistor. Ic2 is probably a dual op amp monitoring batt voltage.
     
  4. ArgusP4

    Thread Starter New Member

    Apr 18, 2015
    5
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    Cool! Totally missed that chip. I definitely should have looked that up. What would your course of action be? My first thought would be to cannibalize the board and use the components that test out to build new. But considering my level of experience I bet there is an easier way to track down the fault and skip or replace that section.
    Argus
     
  5. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Looks like on the board below the 1997 date stamp is where a throttle pot was connected. You have the throttle control correct? I believe beyond that Dogydave pretty much sums it up as to reverse engineering the board and make a drawing.

    I would not gut the board to reuse components. That board has a small parts count of very inexpensive parts. I would look to repair the board. A matter of drawing it out and understanding how it is supposed to work. You know you have a 556 dual timer (two 555 timers on a single chip) and a Google of 556 PWM Circuit will bring up dozens of similar circuits. That should help.

    Ron
     
  6. ArgusP4

    Thread Starter New Member

    Apr 18, 2015
    5
    1
    Yup, I do have the Pot. And yes, thanks to Dave I have enough info to map the whole circuit. So the question now is, What is the easiest way to find the broken component or area of the board?

     
    Dodgydave likes this.
  7. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,974
    744
    your best way is to draw the circuit out, that way you can see how it functions ,then use a dvm to check the voltages and signals.
     
  8. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Once you create a drawing you should have some idea of how the circuit works. For example the throttle pot likely has one end tied to a + fixed voltage and the other end to ground. So look at the pot wiper which should provide a variable voltage as the throttle is moved. Check power to your chips like the 556 for starters. If you use Google as I mentioned you will likely find circuits similar to what you have, that can help. I am guessing you don't have an oscilloscope but if you have a DMM you can do some good logical troubleshooting from the drawing you make. Looking at your pictures nothing seems to jump out as obviously burned or broken. Some isopropanol alcohol and a used old toothbrush can be used to further clean the board and inspect for small cracks or bad solder joints.

    Dogydave is typing faster than me. :)

    Ron
     
  9. ArgusP4

    Thread Starter New Member

    Apr 18, 2015
    5
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    Awesome, that's exactly what I needed! I was thrown about the lack of burns/melted stuff and got a little overwhelmed. I do have a good DMM, Santa didn't bring me an oscilloscope yet :p. I'll start with your suggestions and see what I find.

    P.S. I have had to delete many a forum post over the years because I was too late and some 600 WPM secretary beat me to it haha. Thanks for bearing with me Reloadron!
     
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