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need help with just bought cobra 2000gtl

Discussion in 'General CB Services Discussion' started by 1iwilly, Aug 2, 2020 at 9:36 PM.

  1. 1iwilly

    1iwilly Active Member

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    i pick up a cobra 2000 gtl that needs TLC the 1st issue is radio dead keys 4 watts but swing downward when modulation is applied.
    on ssb it shows no power on either lsb or usb i change tr41 with an updated one i also change driver 2166 and 1969 from a working radio just for testing purpose.the issue is the same weather on ac or dc power
    2nd issue they change the 5 pin mike jack for 4 pin but you can even go pass 9 o'clock before it starts squealing and oscillating
    3rd issue clarifier was modded trying to see where wire go to put it back to stock as i don't have a schematic yet
    any help or guidance is very needed as i need to fix mike jack 1st thanks


     

  2. red97k1500

    red97k1500 Well-Known Member

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    Can you post some pictures? I have an unmodified 1983ish 2000 gtl that I can post some pictures of.
     
  3. nomadradio

    nomadradio Analog Retentive

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    The 5-pin mike jack HAD two separate ground circuits. One on pin 2, the other on pin 4. The pin 2 ground is to carry ONLY audio from the mike. The pin 4 ground is for the keying circuit in transmit, and to complete the speaker ground in receive mode.

    When you combine these two separate ground circuits you get feedback problems. That's why they were kept separate in the first place.

    Putting the 5-pin socket back in the radio is the simple cure. We use a relay to carry the pin 4 current when the customer insists on a 4-pin mike socket. That keeps the two ground circuits separated. Don't have a 'kit' for sale to do this.

    As for the clarifier, too many possibilities to list. More than one way to mess it up.

    Would help to know what the starting point is in your radio.

    A radio that modulates the AM carrier, but won't show any power on SSB is not a common fault. Not sure about that one.

    73
     
  4. 1iwilly

    1iwilly Active Member

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    thanks, guys ok here some pic clarifier mod and the mic jack there is a brown wire from pin 1 going to the headphone jack they cut the wires so tight from where they go on board for me to see where they go i know the blue one goes by r44 the orange by r174 but i can't see where the yellow goes and the brown then the red one too
     

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  5. walterjn

    walterjn Well-Known Member

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  6. 1iwilly

    1iwilly Active Member

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    thanks it just makes harder going back and forth from computer to garage a pic i clearly see the color and where it goes on the board

     
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  7. red97k1500

    red97k1500 Well-Known Member

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    4DD1A35A-E33D-4033-96B1-C1FB37FA8BC5.jpeg I’m not sure if these pics are good enough to help you or not, when I get some more time I can try and take some better ones 4273C292-1D10-4B10-9748-A81EC3696360.jpeg
     
  8. 1iwilly

    1iwilly Active Member

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    thanks a million, red97k got it back to stock now the only final issue is they took out the factory 5 pin jack and made it a 4 pin but it's not right it squeals if you go past 12.00 o'clock and you can hear a slight like oscillation sound on the external speaker like if i put at 9 to 10 oclock with a 1000 hz tone i can see 12 watts on ssb but when doing it with voice it barely does 8 watts yes i tried 3 other mikes if you look at image pin 1 which is shield on a 4 pin radio you see the brown wire where they have it going too
     

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    #8 1iwilly, Aug 4, 2020 at 12:19 AM
    Last edited: Aug 4, 2020 at 2:51 AM
  9. nomadradio

    nomadradio Analog Retentive

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    So where is the black ground wire from the mike-gain control? Hot side is red, ground side is black as a rule, leading to that control. Would go to pin 1 of the 4-pin socket.

    Brown wire attached to the headphone jack should be the receive wire, pin 4 of the 4-pin socket.

    Looks like someone before you got pretty corn-fused.

    73
     
    NZ8N and walterjn like this.
  10. 1iwilly

    1iwilly Active Member

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    the red is pin-2 =audio on 4 pin jack on 5 pin jack is pin-1 =audio ok so i will try a board groud to mike gain control

     

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