component (resistor?) missing - replacement

Discussion in 'General Electronics Chat' started by ArchillesElbow, Jan 31, 2013.

  1. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Hi...
    while soldering this component dropped out...
    does anyone know what it is and what it can be replaced with?

    (the component labelled "antenna port")

    its actually of a video transmitter - a 5823 video transmitter
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    The small grey box is what fell out? That is most likely a capacitor.

    Do you have the part that fell off?
     
  3. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Nope the sneaky thing fell off when I wasn't looking.. What I know is that it has a direct trace to the antenna signal pad where the antenna is soldered.. Is it a capacitor u think? It looks whitish?
    If it is a capacitor (tantalum?) then can I just substitute it with another one that looks like it? I have other boards (not the same type ) lying around
     
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    Even though they are the same size, that doesn't mean they are the same value. When parts get that small, there just isn't room to put markings on them.

    Do you have a meter to measure capacitance of the nearby capacitors of similar shape/size/color? If you are lucky, they used the same value several times to simplify the number of reels needed in placement. It's then a matter of trying one, soldering carefully, and testing to see if it works.
     
  5. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Would a multimeter measure the cap?
    There is another cap just below it and I can measure that one perhap
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    No chance you can just guess its value. If it is in series with the antenna it is probably a few pF to tens of pF. With enough understanding of antennas one could maybe calculate its value. You cannot guess its value from its form or appearence. There are thousands of SMD caps that look exactly equal.

    A multimeter with capacitance measurement will give you an approximation of its value. If it's in the pF range it will be a very rough approximation. Unless you have a very good multimeter.
     
  7. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Nope I just checked my multimeter can't calc this..
    What happens if I put the wrong capacity cap in?
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    The wrong value could result in reduced range, frequency shift, distorted output, or not work at all.

    I'd suggest a very thorough search of your work area.
     
  9. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Searched for a day...I'm worried it might have gotten stuck on the solder tip..I didn't see it and it got wiped off on the sponge inadvertently.... Coz I can't see this tiny thing anywhere..
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    If this is a common modification, you could check with other people who have done the mod and see if any of them know the type/value/rating of the missing component.

    If you are unable to find it, I don't have any other ideas to help.
     
  11. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Nope it isn't..
    Actually I put this transmitter on a tiny micro quad that I'm aiming to fly a kilometer and back via the video tx.. I have gotten half that distance and lost the rc connection which made the quad crash... Bending the antenna of the board and taking the solder pad with it... Not many people have modded it this way... The video tx forums don't know...

    I will try with the caps I have lying around..maybe the will work maybe not,
    I already ordered another board anyway,,

    One last question... How do I know which side is pos on the capacitor? Does it have a line or some marking?

    Thanks for all the help so far!
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    The smaller value caps (nano to pico farad) are typically ceramic or film caps, which are NOT polarized.

    Only Tantalum and Aluminum electrolytics are polarity sensitive (very sensitive). These are typically used in values > 1uF. Below that, their parasitic components overcome the actual capacitance, while different dielectrics perform well in that range, and aren't polarized.
     
  13. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Since this has no markings I'm going to assume there is no polarity and going in guns blazing lol
     
  14. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Take a clearer picture of that area and mark where exactly this capacitor was.
    Maybe we can then find out from it's position in the circuit and the datasheet of the transmitter chip what value it should have.
     
  15. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    I doubt you can get 1km at 5.8GHz, especially if there are some obstacles.
     
  16. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    If you haven't vacuumed yet, go round with a magnet. A lot of SMD components can be picked up by one. I'm always dropping them and the magnet finds a lot of them for me.
     
  17. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488

    Good idea, just tested it with the little ceramic caps... It works.:)
     
  18. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Couldn't find the cap..but did find aNother older 2.4ghz transmitter... It had a similar cap.. I soldered that on and it works...
     
  19. ArchillesElbow

    Thread Starter New Member

    May 2, 2012
    26
    0
    Remember it's in the air... I achieve 3kms with the same setup and vtx on my larger planes...
    The antennas are specially made for this...
     
  20. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    Ah ok, I thought it would be used in urban areas behind buildings etc...

    Nice you have it working again. Even if it's most likely not the same value you replaced it with.;)
     
Loading...