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2517 (mosfet version help)

Discussion in 'CB Radio Modifications' started by n4dxx, Apr 18, 2018.

  1. n4dxx

    n4dxx Member

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    Ok guy's i have a 2517 with an issue i have never seen before..Got this radio from a friend who bought it new never been hacked or anything..He had a very high swr and the radio was getting reports of distorted audio and carrier level jumping..Well i have the radio on the bench and the collector voltage on the 2sb827 regulator is going crazy from like 0.78 volts up to 4 volt's when it hit's around 4 volt's the carrier will come up but then it goes away and it does this rapidly..I thought he may have damaged a mosfet (Pulling Current from the regulator with a short to ground)But after replacing all the mosfets pre driver and regulator nothing has changed.The pll seems very stable and i have a steady rf according to my scope driving the mosfets also have checked for any cold solder spots and no joy there either.and the rf power control it's fine as well.Darndest thing i have ever seen..So after 8 hours of digging i need your help..Thanks for any input..


     

  2. midnight special

    midnight special Well-Known Member

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    check and make sure the mike plug circuit board is grounded good,,, even re soldering it if needed and make sure the screw that holds it to chassis is tight,,, to get to the board you have to take the face plate off,,,,,
     
  3. nomadradio

    nomadradio Analog Retentive

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    A check of the 9-Volt regulator would be good. If you have a 'scope, watch the center leg of Q37 to see if it jumps or falls when the transmitter is acting squirrelly.

    The only other thing that comes to mind would be a damaged diode in the mode-select lines that come out of the mode selector switch. A transmit function that's only being partly turned on can cause oddball symptoms.

    What does this radio do on SSB transmit?

    If you haven't checked Q53, Q54 and Q55, you might find a marginal failure in one or more of those three. Those transistors don't always fail as a dead short or dead open circuit.

    Do you have a way to check the driver and finals? Testers that will check a MOSFET have gotten pretty cheap on Chinabay.

    73
     
  4. n4dxx

    n4dxx Member

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    Yes i have checked all mosfets and voltage reulators with a atlas dca 55.I was wrong SSB seems normal it just does this in am mode i have replaced all q53/54/55 and q37 seems normal everything is steady ..Thanks for all the reply's
     
    #4 n4dxx, Apr 18, 2018
    Last edited: Apr 18, 2018
  5. OldTech03

    OldTech03 Active Member

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    Could have been a cold solder joint cured by replacing all those little three leggers? Just sayin!
     
  6. n4dxx

    n4dxx Member

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    Don't think so it's never took me this long to find a cold solder joint..I have a microscope and i have looked it over very well nothing amiss that i can see..
     
  7. OldTech03

    OldTech03 Active Member

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    OK! Sorry, Me Bad, My Bad, My dumb, My ?
     

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