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2000 cobra

Discussion in 'General CB Services Discussion' started by Jerry Davidson, Jun 9, 2019.

  1. Jerry Davidson

    Jerry Davidson New Member

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    I direct injected my cobra 2000 and lost my receive . I was told that I needed a relay, but don’t know what parts or where to install. Anyone know? Thanks


     

  2. loosecannon

    loosecannon Sr. Member

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    can you describe your setup, like how you key the radio, and how and where you inject the audio?

    the more details the better.
    LC
     
  3. nomadradio

    nomadradio Analog Retentive

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    You'll need to supply more detail than that before anyone can make sense of what may have happened.

    The phrase "direct inject" isn't just one thing, there are several ways to accomplish this. Some of them require a way to shut off your direct audio input while receiving. Pretty sure that's what the "relay" advice is about.

    Other hookups do not require a relay to shut off the external audio source.

    My experience has been that any time a modification is made to a radio there is the risk of an unintended consequence.

    Unintended, like making a mod to the transmit, and finding that the receive no longer works.

    First thing to find out is if the meters still work on this radio. When a Cobra 2000 gets to be more than 25 years old, the pointers on the two meters can get stiff and seize up. If they're stuck, you can't tell what the receiver might be doing

    What makes this important is to find out if you see the receiver meter kicking around from channel chatter and noise, or if the receive meter just stays down at zero. If it's kicking around, this means your receive problem is in the audio. And if the meter stays at zero, that problem is farther upstream towards the antenna.

    Have a VERY close look with a very-bright light and a magnifier at the region of the circuit board where your mod was installed.

    The single most-common cause of this "unintended" fault right after a modification is installed will be a small blob or splash of solder that has bridged across two separate foil pads on the solder side of the circuit board.

    Only takes one tiny short like this to shut down the receiver.

    Most important first detail is to find out how much of the receiver is disabled.

    Is the S-meter dead? Or does it still move on channel noise?
    73
     
  4. 357magnum

    357magnum Sr. Member

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    Cobra 2K meters stick ? Tell me it ain't so !:whistle:(y):) Mine need replacing now . One anyway .
     
    kaos513 and undertaker like this.
  5. Jerry Davidson

    Jerry Davidson New Member

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    Nomadradio I removed c174 took a 10uk 50 volt cap and soldered positive leg of cap to positive hole of c174 negative side of cap to center of on/on switch. Negative hole of c174 to one side of on/on switch. Then I used quarter inch plug wire positive side to other side of on/on switch. Negative side to board ground. Audio works and no distance on receive
     
  6. 357magnum

    357magnum Sr. Member

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    Jerry , lots of smart guys on here ! So needless to say I follow all 2k posts especially as I am the proud owner of one I couldn't afford when they came out new !;)
     
  7. Jerry Davidson

    Jerry Davidson New Member

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    I am a proud owner too I have wanted one for years. I am just trying something new to see if I like it. I have been successful with hifi on my cobra 142 but lost my receive on my 2000 not all together but distance is what I lost just looking for a little help. If I could afford it I would pay someone. But I have 4 kiddos to feed in skip land I go by 47 Missouri bandit
     
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  8. nomadradio

    nomadradio Analog Retentive

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    So the Cobra 2000 will still receive, but only strong signals? Won't hear the weak ones?

    Do I have that right?

    73
     
  9. nomadradio

    nomadradio Analog Retentive

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    Do you have any way to put a steady signal into the Cobra's receiver?

    I don't think your direct-inject mod is likely to be part of the problem. The hookup for C174 is not anywhere near parts of the receiver that could reduce its sensitivity.

    Unless maybe you, ah, "splashed" a glob of solder onto the pc board in the receiver section.

    But when the sensitivity of a receiver drops all at once, the first thing I ask is "was the antenna connected during a storm?"

    Lightning can strike a neighbor's tree, or a utility pole down the road and still cause a destructive surge in your antenna.

    The reason for that steady signal source, one you can hear in the 2000 is to see what happens to the alignment adjustments.

    Any of them that do not show a peak point to a problem in that section. If the slug-tuned coil that's the first stage where the antenna feeds into the receiver shows no peak at all, this suggests a surge came down the coax.

    Another common failure is seen in the 'cans' with the small-diameter tuning slug. When the capacitor inside the can goes bad, the slug will now appear to peak with the top surface of the slug dead-flush with the rim of the opening in the top of the can. When you see this, it's not really a peak. It's just the end of travel for that slug. Continuing to turn it counterclockwise will cause it to extend above the rim of the hole. This will have the effect of 'reducing' the coil's inductance. Same as turning it clockwise, so that it recedes inside the can. This "dead flush" position of the peak is not really a peak in the normal sense. A true resonant peak will always be one turn or more below the rim of the opening.

    But yeah, attempting alignment is a diagnostic tool. That's what I would do next.

    73
     
    357magnum and Shadetree Mechanic like this.
  10. Jerry Davidson

    Jerry Davidson New Member

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    Ok thanks. My antenna and coax seems to be fine. I am getting the same signal on my 142 as I always have. But I will check for splash and L3,4,5
     
  11. 357magnum

    357magnum Sr. Member

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    Btw Jerry , Welcome to the forum ! Is that an older Maco 750 I see in your Avatar ? Two words .... " I likey " !;)
     
  12. Jerry Davidson

    Jerry Davidson New Member

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    Yes it will fly
     
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  13. M0GVZ

    M0GVZ Sr. Member

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    Another perfectly good CB killed by someone doing something they know nothing about and without the test gear or knowledge to put it right again to try to achieve something which has absolutely zero benefit.
     
  14. 357magnum

    357magnum Sr. Member

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    MOG , If I Agree or Disagree , if people want to make Fish Tanks out of them .... Hey It's theirs !:whistle:;):)
     
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  15. Jerry Davidson

    Jerry Davidson New Member

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    357magnum thanks for reply I just can’t afford all the stuff needed to diagnosed properly. Probably should not have done it. But I just wanted to do something different I can always put it back. Still can’t find no answers. Rodger
     
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