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Cobra 142 GTL receive issues

Discussion in 'Amateur Radio Modifications' started by TruckerKevin, Feb 18, 2018.

  1. TruckerKevin

    TruckerKevin New Member

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    I inherited a cobra 142GTL that has sat for 20 years. Right off the bat I noticed that its volume is not as loud as the other one I own and currently in use. It also has very poor receive, as in I cant hear anyone unless its my other radio in the other room. It does have static, so it's not like a squelch problem. Has excellent transmit.

    Its like, have you ever had a cb turned on but no antenna hooked up, but when you hook the antenna up it gets louder and the static changes? This radio don't have that. It sounds the same hiss, with or without an antenna hooked up. Like it's not getting a signal

    I had a cap kit that I was going to use for a different radio, but I used it for this one hoping to shotgun the issue, but no dice. Caps all replaced but the issue remains.

    I was thinking there was some sort of amplifier issue on the receive side. I do have a washington that I can rob parts off of.



    Does anyone have any clues on where I should look first? I can hear my wife talking to me on it from the driveway but as soon as she gets down the street its gone.
     

  2. loosecannon

    loosecannon Sr. Member

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    have you aligned the radio?
    LC
     
  3. TruckerKevin

    TruckerKevin New Member

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    No do you think it is just a matter of a simple alignment?
     
  4. loosecannon

    loosecannon Sr. Member

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    it's the first thing any tech you send it to would try.

    the alignment can point out the trouble spot many times.
    LC
     
    Shadetree Mechanic likes this.
  5. nomadradio

    nomadradio Analog Retentive

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    The receiver can lose its sensitivity in more than one way.

    Kinda like "car won't start". Not a very complete description.

    If it spent any of those years in an unheated space, it will end up with condensed moisture inside a few days a year. Can't avoid the "morning dew" in an unheated space, unless you're in a desert. A damp basement presents the same risk of metal oxidizing inside those parts.

    Alignment can be a troubleshooting tool. If someone simply twisted a bunch of tuning slugs, this will bring the radio back from the dead.

    And if condensing humidity has damaged those small square 'cans' with the tuning slug in them, the behavior of that tuning slug can point you to the cause of a fault. Any of the ones with the skinny slug that appears to peak with the top of the slug dead-even with the rim of the hole deserves further scrutiny. The correct setting for the small slugs is at least one whole turn below the rim of the hole. Usually a couple or more turns below the rim.

    A repair guy who charges for labor will probably start with the alignment procedure just to sort out the extent that "tweakeritis" is causing the problem, or if some component, or two, or five has gone bad and broken down.

    No other effective way to find out.

    73
     
    Shadetree Mechanic likes this.
  6. TruckerKevin

    TruckerKevin New Member

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    That makes good sense, thank you for the logical answer
     
  7. ahh

    ahh Member

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    Hi, Trucker Kevin. Did you ever figure out the problem? I might be fuzzy in my remembering, but seems like I had similar problem with my President P400, which is a clone of the Uniden Washington. Also, my President P400 has the same circuit board as your Cobra 142, SO, except for the outward appearance (and an SWR meter the P400 and Washington did NOT come with, we have basically the same radio.

    Anyway, I lucked out with mine, and the only problem with it was the audio chip in it went bad. Had it replaced, and 15 years or so later, it works fine. Before that repair, and to this day, I have never had a problem with that radio. Good luck and have fun.
     
  8. TruckerKevin

    TruckerKevin New Member

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    Holy cow, the audio chip is one of the things I suspected was wrong. I have actually acquired a Navajo radio with the same exact issue. I will replace the audio chips and see what I get!
     
  9. Robb

    Robb Yup

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    Sounds like an old radio. Like all old radios, they have cap problems either emerging or already present. Wouldn't hurt to test all of the caps in that circuit and see if any of them have gone south. Seen that a few times . . .
     
  10. TruckerKevin

    TruckerKevin New Member

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    I forgot to report that I recapped the whole radio with Klondike Mikes kit, testing it along 2 at a time. Was a no go on this radio anyway
     
    Robb likes this.
  11. loosecannon

    loosecannon Sr. Member

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    TK, did you align the receiver after re-capping the radio?

    if not, try this. set the radio to channel 20, AM mode. RF gain all the way up. volume set so you can hear static from the speaker. (you might be turning the volume down as you peak the coils) no antenna connected.

    using a plastic tool (NO JEWELERS SCREWDRIVERS) peak L3, L4, L5, L6, L7, L8, L9, and L10 for maximum static.

    you should notice a definite position of each coil that relates to a maximum of volume coming out of the speaker.

    If you find a coil that doesn't seem to do anything, stop there and post back which coil it was.

    my guess is that your first RF amplifier transistor might have gone bad, and this is our first step in confirming that.


    here is a link to a page that has the service manual for a Teaberry radio that is the same on the inside as your 142GTL. you will find lots of good info and learning opportunities in there.
    http://www.cbtricks.com/radios/teaberry/stalker_xv/index.htm

    good luck!
    LC
     
    #11 loosecannon, Apr 15, 2018
    Last edited: Apr 15, 2018
    Shadetree Mechanic likes this.

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