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Cobra 2000 GTL weird issues

Discussion in 'General CB Services Discussion' started by Kracker, Nov 13, 2017 at 4:13 AM.

  1. Kracker

    Kracker
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    I just got this and it seems to have a few issues.
    1- When listening, there is static but no signal or voice receive. I can however hear a test radio 1 foot away. TX works. and PA works. i was told to replace all electrolytic caps and i did. no change, good anyways.
    2- after changing the first few E-caps it started a weird issue. when i shut it off, the LCD displays stay about 5% lit, just enough to notice.
    3-i noticed that i have +12v at the chassis in AC and DC mode.
    4-i was told to throw in a Receive Kit w/SSB Transistor Upgrade from ebay. i did, now my freq counter does 2 things. first, it cycles all over when radio is off. second, when i key up it changes frequency.
    for a totally unmolested unit I'm ready to fill it with tannerite and go boom!
    Where to start? There are NO CB shops around.


     

  2. nomadradio

    nomadradio
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    Out of all these details I can explain only one of the symptoms with the info you supply. The channel digits are glowing with the power switch 'off' because the two incandescent lamps behind the two meters are blown. The resistance of those two bulbs serve to shut down any remaining voltage on the radio's circuit board. Reason for this is that the Cobra 2000 power button doesn't open the hot side of the DC power supply, but instead opens the ground side. Since the clock/counter is still powered, there is a so-called "sneak" path from the power inside the counter to the ground circuit of the radio's circuit board. Those two bulbs serve to "pull up" the radio's ground to a high enough voltage to shut off the channel digits. When the bulbs go bad, you'll see the 'ghostly glow' when powered off.

    If it was broke before you replaced all those caps, it was still broke after they got replaced. Have you had a close look at the solder side of the circuit board with a bright light and magnifier? It's easy to bridge a bit of solder across the gap between solder pads.

    If you had told a mechanic "my car won't start" and asked him how to get it running, he might first ask if you have any tools to work with.

    That would be a good place to start. Receiver problems can be a major pain in the neck to track down if you can't push a signal into it and then make a measurement.

    How good are you at reading a schematic? Big help when trying to follow the progress of the signal through the receiver and pin down where it's being stopped.

    Might be possible to tear down a motor, rebuild and make it run again with only screwdriver and a crescent wrench.

    Might not. But here's the annoying part. The master mechanic with the instructions already in his head might pull it off. But the shade-tree guy who hasn't done it before is the one who will benefit most from a step-by-step manual with pictures and a full set of tools.

    73
     
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  3. 9C1Driver

    9C1Driver
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    I would skip the receiver kit, a 2000 is such a fine radio a proper receive alignment will do the trick.
     
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  4. sonoma

    sonoma
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    Well Kracker you just received some of the best info around.. Nomad is about the best tech I know of from years of reading his messages. . he always puts in the little quirk notes so pay attention to what he says. the diode trans upgrade is fine for the 2000 as long as it was just the 1n6263 diodes and trans to upgrade the diodes.
    the freq counter change from TX to RX could just be the radio is not aligned properly.
     
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  5. Kracker

    Kracker
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    Well i installed all new bulbs. No change...
     
  6. nomadradio

    nomadradio
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    When you hear the radio a foot away, does the S-meter move?

    Do you have alignment tools with non-metallic tips to fit the internal adjustments?

    Any idea how many unsuccessful attempts have already been made to fix it before you got the thing?

    73
     
  7. Kracker

    Kracker
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    Yes it moves
    No
    No idea
     
  8. nomadradio

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    Not gonna get too far without basic tools. One reason you'll frequently see the advice to "try aligning the radio" is the practice some folks have to just twist adjustments randomly.

    If a radio has been simply "screwdrivered off the air" this will fix it.

    Unless the brittle ferrite/ceramic tuning slugs inside those 10mm metal cans have been cracked in the attempt. They'll seize up against the inside of the coil form when this happens. Only a small pain in the neck for some of those. Some of the "cans" with the small-diameter tuning slug have an open bottom. Unsoldering it from the pc board exposes the unbroken tool slot on the underside of the tuning slug. With luck and finesse, the slug can be backed out the under side, broken fragments removed and threaded back into the hole from the top opening. Re-installing the coil will now permit it to be adjusted properly.

    This tool from ChinaBay fits the small-diameter tuning slugs.
    https://www.ebay.com/itm/0-4x1-3-Sl...375999&hash=item2a7ab375d2:g:HxIAAOSwImRYmWP0

    There has to be a YouTube vid out there that explains how to align a Cobra 2000 receiver.

    Can't remember ever looking for one.

    73
     

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