preamp component smoked - RF Concepts 2-417

Discussion in 'Amateur Radio Amplifiers' started by KD2QED, Nov 17, 2019.

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  1. AA7QQ

    AA7QQ Ham Member QRZ Page

    One more wider shot of the whole board. Or at least that half. It's somewhere near RY2, I am guessing. Just need to see where that trace Tees off to.

    Ed
     
  2. AA7QQ

    AA7QQ Ham Member QRZ Page

    Also, when you turn on the pre amp switch, do you hear the relay click? This will tell us if it is in the relay driver circuit, or the preamp, itself.
    Otherwise, TX & RX are unaffected?

    Ed
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It looks like it may be L104A, If it is connected to RY3 relay coil, It looks like it is.

    upload_2019-11-18_6-30-38.png

    What ever it is, It needs to be lifted off the board more, Looks like it may have shorted to the foil trace below it.
     
  4. AA7QQ

    AA7QQ Ham Member QRZ Page

    Looking at this picture I found on Google http://medan-radio.blogspot.com/2019/08/rf-concept-2-417.html
    I see that it is on the trace that goes to the preamp switch, I think. Seeing a diode come off of it, tells me that it in the area of R15, r16, but most likely is R14. Follow the trace that goes to the switch to confirm. See which way the diode goes.
    This is my best guess without seeing the bottom, or a more detailed pic of that half of the PCB.
    Take a few pics of that half with the wires moved in different directions. Take them from straight above.
    Or, just confirm that the trace from the Preamp switch goes to the burnt part.

    Ed
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Yes, A wide camera shot would be much better. Zoom out, Not in. ;)

    It is hard to see from here.

    It should be very easy to tell how it is connected.
     
  6. KD2QED

    KD2QED XML Subscriber QRZ Page

    It used to click but no longer does. TX and RX still working without issue.

    Here are a few more pictures detailing where I am at:


    20191118_082328.jpg 20191118_082341.jpg

    the full board:
    20191117_163918.jpg
     
  7. KD2QED

    KD2QED XML Subscriber QRZ Page

    The traces also run under the yellow/clear thing, not sure what it is, just south of the relay. It meets a diode and resistor there.
    20191118_084151.jpg
     
  8. KD2QED

    KD2QED XML Subscriber QRZ Page

  9. AA7QQ

    AA7QQ Ham Member QRZ Page

    I am sticking with R14 8200 ohms, or 8.2K. I am guessing the inductor is L2, in the preamp circuit. The resistor that splits off to it is R19.
    So, an 8200 ohm should be replaced, in my opinion.
    I am just baffled, as to why that part went. I am no expert, but see nothing that would pull enough current.
    I personally would pull the board & check the underside for a loose solder blob that may have shorted it to ground. Also, trim any bottom leads that may seem long.

    Ed
     
  10. AA7QQ

    AA7QQ Ham Member QRZ Page

    Well?

    Ed
     

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