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Thread: Help me repair my V-FMT212R

  1. #1
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    Default Help me repair my V-FMT212R

    Hi, have a V-FMT212R. Worked great last year. This year no worky.
    Found the connector to my antenna had a short in it.
    So im guessing the driver got fried.

    Anyone know anything about the electronics inside it?

    There is 1 component in there i am suspecting is the power driver, but i cant confirm. Looks like a typical 3pin power transistor. Marked "V3" and "33" and cant seem to find what it is on google. Anyone can help at all?
    Or maybe its a surface mount diode somewhere that fried?? Cant easily see any otjer SMT tramsistors and all the other chips are so small so im guessing those arent the problem?

    Going to scope it out at work but im not too confident i can figure it out.

    Any help appreciated. Dont want to go back to those cheap car xmitters and prob gumma take at least 2weeks to get a new V-FMT212R in the door?


    Help please!!!

  2. #2
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    Default Re: Help me repair my V-FMT212R

    I'm not sure a simple ohmmeter test is valid for an FM output measurement. If it uses a small coil which to an ohmmeter is a short but to FM frequencies it can be 50 ohms or more. A better test would be to terminate the FM output with a 50 ohm resistor and then use a signal strength meter to see if there is a carrier output with no audio modulation. A spectrum analyzer would be better.

  3. #3
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    Default Re: Help me repair my V-FMT212R

    dont have a spectrumanalyzer. you dont think an oscope will work while device is powered?

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    Default Re: Help me repair my V-FMT212R

    Quote Originally Posted by MrDudeMan View Post
    Hi, have a V-FMT212R. Worked great last year. This year no worky.
    Found the connector to my antenna had a short in it.
    So im guessing the driver got fried.

    Anyone know anything about the electronics inside it?

    There is 1 component in there i am suspecting is the power driver, but i cant confirm. Looks like a typical 3pin power transistor. Marked "V3" and "33" and cant seem to find what it is on google. Anyone can help at all?
    Or maybe its a surface mount diode somewhere that fried?? Cant easily see any otjer SMT tramsistors and all the other chips are so small so im guessing those arent the problem?

    Going to scope it out at work but im not too confident i can figure it out.

    Any help appreciated. Dont want to go back to those cheap car xmitters and prob gumma take at least 2weeks to get a new V-FMT212R in the door?


    Help please!!!
    If you shorted the antenna connector and powered up the unit, you probably fried the final transistor. If that's what you're referring to when you say "driver," then you are correct. That component will have to be replaced, as there's no way to repair it. If you can get the part number off the transistor, then mouser or digikey may have it. You'll have to be handy with a soldering iron as well. Good luck.

    --Mike

  5. #5
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    Default Re: Help me repair my V-FMT212R

    Quote Originally Posted by MrDudeMan View Post
    dont have a spectrumanalyzer. you dont think an oscope will work while device is powered?
    Well, if your o'scope can go up to 100 MHZ it might see something. A field strength meter may also be useful like this; https://www.youtube.com/watch?v=y-x2tVGPiE0
    How are you testing the FM transmitter? Is it possible your input audio is in mute mode?

  6. #6
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    Default Re: Help me repair my V-FMT212R

    i didnt change settimgs on xmitter and wasnt working which lead me to find the short.

    fixed short still no worky.
    opened up xmitter app and it show realtime audio input level and there was signal which changed when i changed volume.

    i think scope at work is 100mhz. and im using 91.5 so i guess it should work. hoping i can find where the signal disdapears near tje output and infer which component is bad. worried the 3pin transistor thing is not the driver cuz its not very close to the antenna output side of the board. was hoping someone here was familiar with components on this xmitter.

  7. #7
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    Default Re: Help me repair my V-FMT212R

    You can post a picture of the FM board and see if members here can recognize certain features as to whether there is an external output transistor. It could be in the FM chip itself, thus not accessible.

  8. #8
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    Default Re: Help me repair my V-FMT212R

    Quote Originally Posted by MrDudeMan View Post
    i didnt change settimgs on xmitter and wasnt working which lead me to find the short.

    fixed short still no worky.
    opened up xmitter app and it show realtime audio input level and there was signal which changed when i changed volume.

    i think scope at work is 100mhz. and im using 91.5 so i guess it should work. hoping i can find where the signal disdapears near tje output and infer which component is bad. worried the 3pin transistor thing is not the driver cuz its not very close to the antenna output side of the board. was hoping someone here was familiar with components on this xmitter.
    There are loads of transmitters on amazon that you get get in just a couple of days. Your unit may be beyond repair.

    -Mike

  9. #9
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    Default Re: Help me repair my V-FMT212R

    As an rf technician I could offer the following tips:
    Lower wattage transistors could look like any kind of transistor, higher wattage output rf transistors usually have white circular tops made of ceramic or black, 3 or 4 legs about 1/4" wide, incredibly hard to unsolder (since the legs are wide they dissipate alot of heat), a solder wick is useful, one leg will be tied to the power + buss. Lightup is correct, usually measure a short in circuit. With the numbers you have, I dont think that is complete. I doubt you will find the correct part without a schematic or parts list. Then you would have to order one.
    Sorry wish I had better news for you.
    Last edited by aknflyer; 12-07-2017 at 02:07 AM. Reason: added detail

  10. #10
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    Default Re: Help me repair my V-FMT212R

    Quote Originally Posted by MrDudeMan View Post
    dont have a spectrumanalyzer. you dont think an oscope will work while device is powered?
    Well, you could get something like this, RTL-SDR dongle in SDRSharp as demonstrated here... http://doityourselfchristmas.com/for...M-transmitters

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