LED CIRCUIT

Discussion in 'General Electronics Chat' started by RONR11, Mar 8, 2009.

  1. RONR11

    Thread Starter New Member

    Mar 8, 2009
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    Newbe here with a question.
    I have a mustang with a aftermarket sequential 3 light circuit,the circuitboard has burnt out a transistor and I cannot read the type.
    It looks like a simple circuit with only 3 components a 12f629,a vn 920
    and the transistor that I cant read. The seller wants to sell only the kit for $200+. Thanks for any help Ron
     
  2. thatoneguy

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    Feb 19, 2009
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    12F629 is a PIC Microcontroller, VN 920 is a solid state relay.
    Do you have good, clear photos of both sides of the board?

    Does the transistor drive the relay, or a portion of lights?

    Without seeing photos of the circuit board, it's impossible to guess what it might be, and even then, the exact transistor probably won't be identified, but one that should function similar could be.
     
  3. SgtWookie

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    Jul 17, 2007
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    The 12F629 is a PIC microcontroller, made by Microchip.
    The VN920 may be a solid state relay, or other items if it has more qualifiers on the end.
    http://www.st.com/stonline/stappl/p...artNumberSearch.searchPartNumber&search=VN920

    The other item may be a voltage regulator IC.

    The PIC will run on from 2v to 5.5v, depending upon it's clock frequency; a VN920 solid state relay requires >3.5v for a logical high input. So, if the "mystery transistor" is indeed a voltage regulator, it was probably something like a 78x05 (fixed 5v regulator for 100mA, 500mA or 1A output). If it was in a TO-92 package, it's probably a 78L05. If it's in a TO-220 package, it may be a 7805.
     
  4. thatoneguy

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    I totally forgot power. The more I think about it, the more it makes sense, too. Just hope the PIC and it's program didn't die with the regulator.

    The pricetag throws me off a bit, though, and wonder what all is included in the kit, such as custom LED fixtures, etc.
     
  5. SgtWookie

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    Well, it's actually possible that the voltage regulation for the PIC could be just a Zener and a resistor, and our OP didn't notice them (or they could be tiny SMT parts, too...)
    ... and the "mystery transistor" could be another VN920. :confused:

    After all, a sequential turn signal for just three lights would require only two switches besides the original flasher. A single VN920 wouldn't be enough to control two bulbs - unless there is a dual version available that I don't know about.

    Similar kits for older Mustangs (2005 and prior) are running $109 and up on the Web. A bit more searching, and I found them for less, and more... it depends on what all you get with them. Some come as a plug-in harness - it replaces the existing harness. Some you have to cut into your existing harness.
     
  6. RONR11

    Thread Starter New Member

    Mar 8, 2009
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    Thanks to all for your replies, this is only the flasher part of the sequential circuit, it has 3 wires RED which is 12v, GREEN is output and comes out of pin 1 of the vn 920, the other is ground The outer leg of the vn920 feeds the center leg of the burnt transistor
    this board takes the place of a older style flasher.will try and shoot a pic of this setup Thanks Ron
     
  7. RONR11

    Thread Starter New Member

    Mar 8, 2009
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    looking under a bright lite we can make out a FKH21 on TOP and M7 01 or 81 in the middle and a 05 and maybe a 7 on the bottom,the rest is burnt took a meter and traced the following, the collector of the transistor goes to pin 8 of the12f629 base to vcc of vn920 emitter goes to ground if that helps
    Thanks Ron
     
    Last edited: Mar 9, 2009
  8. SgtWookie

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    I don't know how you're identifying collector, base, emitter of the "mystery transistor" before you actually have a datasheet for it.

    FKH21 doesn't match anything.
    Try harder with the M7 01 or 81 in the middle. Perhaps it's an M7805?
    Post photos of both sides of the board.
     
  9. thatoneguy

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    Feb 19, 2009
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    I'm looking at a 78L05, TO-92 case (looks like 2N2222: plastic, half sphere, flat).

    Top Line:
    FKH23 (Fairchild, Date Code)
    MC78L (part number, first half, middle line)
    05ACP (Bottom Line, rest of part number.)

    I believe we are looking at the same thing. I'm guessing "transistor" is assumed since it doesn't have a heatsink tab like TO-220/7805.

    Correct pins, Looking at the flat spot, left to right, are Output 5V, Ground, Input.
     
  10. SgtWookie

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    I think you're onto something, thatoneguy ;)

    Now our original poster needs to figure out WHY that regulator got fried. Just a wild guess here; if there were no caps on the input or output of the regulator, that could've caused high frequency oscillations and high currents.
     
  11. RONR11

    Thread Starter New Member

    Mar 8, 2009
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    First: let me thank both of you guys for working with me on this.Oneguy has the right thought ,it's a old school transistor half round and facing the flat that is were I got the leg id .there is no caps in this circuit only the 3 components and 3 resistors. Not sure why it burnt out but it was covered in shrinkwrap and open at one end and when cut open it had white powered around the ic chip ,looks like moisture to me ,the leg the burnt was the emitter.This car is stored in a damp enviroment and was thinking that maybe being under the dash it drawed moisture .This is a older mustang with 3 leds on each side ('shelby type). Each led has it's own circuit board and numbered as not to install in the wrong position. I did put a stock flasher in to test and all the lights work together,no sequential so I'm guessing this is only a flasher? Ron
     
    Last edited: Mar 10, 2009
  12. SgtWookie

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    That style case is an industry standard called TO-92.
    Be aware that there can be variations on the pin assignments.

    Interesting. You might consider adding 0.1uF (100nF) caps between input and GND, and output and GND - or at least one on the output.

    As above, refer to the Fairchild datasheet for the correct nomenclature for the pinout. You can download a datasheet from this page:
    http://www.fairchildsemi.com/sitese...mand=text&attr1=&attr2=&t=0&i=sitemap+id&ia=1

    Note that with the flat side facing you and the pins down, the pin functions are:
    Output GND Input
    It's hard to say what the precise function of that board is; their are other boards that you have not told us anything about; except that they exist. It might send pulses to the other boards which may have microcontrollers and other components on them. You should check them over for overheated/burned components. Also pay attention to the wiring; sometimes people mistakenly use "electrician's tape" on auto wiring; the adhesive generally fails inside a couple of years and bare wires touch ground.

    Humid environments are generally A Bad Thing for electronics.
     
  13. thatoneguy

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    The other side of the relay should go to a pin on the PIC

    The PIC is a miniature programmable computer, with an internal oscillator, so one can be programmed simply to put 5V on a pin for half a second, wait half a second, then hold zero volts on the pin for half a second.

    It is powered by the blinker signal, the processor/program starts instantly (well, there is some startup time, but you'd never know in your application).

    If it was damaged, there isn't an easy replacement unless you can describe how this light should blink. From there, we could talk you through programming one for a grand total of about $45 with shipping (for programmer, a couple blank 12Fs, breadboard, and software)


    --ETA: Benefit to doing it yourself is you could make custom blink sequences, faster or slower, etc. Might want to test all of the Solid State Relays as well. Those are what allow the 5V Signal from the PIC pin to switch High Current 12V.

    That is a worse case scenario, 78L05's usually have great protection so they fail open rather than dump 12V to the circuit. Check between the outside legs (output and input) with a multimeter to make sure it reads "open".


    --ETA Again: Definitely add Caps on both input and output side of the 78L05. Usually a 0.1uF on the output side, and a 10uF/25V Electrolytic on the input side. If you use smaller caps 0.1uF/none on both sides, it can oscillate. That is a design error on the part of the seller, unless there are some surface mount capacitors (often tan/green/grey) marked with "104" or similar on the bottom side between the pins and ground.
     
    Last edited: Mar 10, 2009
  14. RONR11

    Thread Starter New Member

    Mar 8, 2009
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    Looks like you guys have it, I took my meter and the center leg does go to ground
     
  15. thatoneguy

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    As long as the outer legs aren't shorted together, there's a good chance the processor is still fine.

    Get pictures of all boards in the setup, both sides, preferably, and attach them to a post or two if needed. From there, quite a bit can be determined if everything is in good focus, and what wires go where are described well.

    Moisture is more than likely what killed the regulator, but I'm guessing the humidity caused another component to fail, which then caused the regulator to fail. The 78L05 cannot supply much current before going into protection, let alone burning, so the failed component may look fine. That's the "hard part" about your problem.
     
  16. RONR11

    Thread Starter New Member

    Mar 8, 2009
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    Thanks oneguy, will try that, also going to look at complete system including tailights for moisture and grounding problems, will post results
     
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