1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice
Dismiss Notice
This forum does not allow a single user to have more than one username. If anyone wants to change their username contact an admin and it will be done. Multiple accounts belonging to the same member will be deleted without warning.

Cobra 29 LTD Green light gone on TX

Discussion in 'General CB Services Discussion' started by Mark A Bradley, Apr 9, 2021.

  1. Mark A Bradley

    Joined:
    Mar 22, 2019
    Messages:
    25
    Likes Received:
    11
    Lost my green light on TX, is it a possible Transistor? Thanks,,,


     

  2. 9C1Driver

    9C1Driver Sr. Member

    Joined:
    Aug 13, 2008
    Messages:
    3,464
    Likes Received:
    1,274
    Does the radio still work like normal? Probably just lost the green bulb.
     
  3. nomadradio

    nomadradio Analog Retentive

    Joined:
    Apr 3, 2005
    Messages:
    4,307
    Likes Received:
    5,422
    Green light is for receive only. Should change to red when transmitting.

    And that's the question. Is the radio transmitting? The missing red light CAN indicate trouble. Might just be a bum LED.

    73
     
    tecnicoloco likes this.
  4. baconater4749

    baconater4749 New Member

    Joined:
    Nov 11, 2020
    Messages:
    6
    Likes Received:
    2
    I need to tune the radio, as the previous owner got crazy with a screwdriver, if you know what I mean.... I was just curious if it was part of the tuning or a bad transistor.
     
  5. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Joined:
    Apr 23, 2018
    Messages:
    4,284
    Likes Received:
    5,120
    Well, the Green Light (LED) turns RED in TX - so it's a Bi-color - but it can be a TRI-Color (Amber-Yellow) when the Mic wiring or the TX keying circuit is goofed up.

    So yes, there's Green for RX, RED for TX, and AMBER for Really Screwed Up...

    The bigger clues on Receive working or Not, is to listen to the radios' noise thru the speaker...

    • turn off ANL and NB for this and turn down the Squelch - you'll hear the "White noise" from the RX section - this is the "noise floor" of the receiver side of the radio - a performance marker.

    This also can help you determine is the Receive is properly balanced by using the "white noise" for a simple check - uniform level across the channels and the channels don't have a "delay" in locking in so you can hear the noise (uniformity) that means the radios PLL is locked and awaiting the Signals to be received.

    upload_2021-4-10_21-5-59.png

    Another set of threads that can possibly provide help...

    https://www.worldwidedx.com/threads/cobra-29-ltd-classic-no-rx-tx-help.253718/page-3#post-716216
    https://www.worldwidedx.com/threads/29-receive.251148/#post-701410
    https://www.worldwidedx.com/threads...e-until-it-warms-up.239208/page-2#post-659837
     
  6. Slowmover

    Slowmover Elmer

    Joined:
    Feb 17, 2015
    Messages:
    4,300
    Likes Received:
    6,369
    If you heard a bell in the distance, your little angel got her wings: now she speaks straight to Heaven. Care in what said — and how — is paramount henceforth.

    .
     
  7. Mark A Bradley

    Joined:
    Mar 22, 2019
    Messages:
    25
    Likes Received:
    11
    Handy Andy and all, thank you for the input,going to give it a whirl, I beleive the Amber light may be for the weather board??? I thought when you turn the weather frequency's on, you get the Amber light, I could be wrong,,,
     
  8. Mark A Bradley

    Joined:
    Mar 22, 2019
    Messages:
    25
    Likes Received:
    11
    Fly away little Angel, nothing around here to get into...
     
    Slowmover likes this.
  9. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

    Joined:
    Apr 23, 2018
    Messages:
    4,284
    Likes Received:
    5,120
    Good observation!

    Not on all radios, Cobra 18 it does, but not all 25's nor the 29's - it would be nice to have a more distinct color to help identify what the radio is receiving - but NOAA blaring out the of speaker tends to remove all doubt on radios so equipped.

    To help, RX light is thru the power supply - R103 a 200 ohm 1 watt resistor, and R113 - a 470 ohm resistor - supply the Green side of the Bi-color led - it's power.

    How does it turn off?

    Look for D20 - find it? On it's banded side, check for continuity to PIN 3 of your Microphone Jack - in RX mode Pin 1 and 4 are shorted at the Microphone. You hear the speaker thru the connection.

    When you key the mike, Pin 4 OPENS, and Pin 3 SHORTS to Pin 1 - now the Pin 3 grounds the TX thru Pin 1 - turning on the TX side, and D20 - "dumps" all the power going to the Green side of the Bi-color LED - to ground - no power Green Off, when you have TX. - The Red side of the BiColor LED is on powered by the TX switch turned on by Pin 3 - so the radio transmits (if the PLL says' it's ok to do so...)

    Although not impossible, the "Green" side of the Bi Color LED can go out (burn out - blow open) due to a power surge or wired backwards sort of connection to the power plug - the reverse voltage can blow out that LED's side that it was connected to - this includes if ever mic connector Pin 3 if the power was hooked up backwards and the mike was keyed - fry that little chip in a blink of an eye. Does not always affect RED - it usually survives because it wasn't in the surge path.

    So if you can verify voltage going to it, thru R113 (verify R113 is not open - ohmic 470 ohms across the resistor here)
    • - and if the line to the LED is near zero in voltage - then the green diode side of the LED is shorted out and that means the whole LED is replaced)
    • If R113 shows about 1.7 volts - and it still won't light, it's (LED) probably bad (Green Chip blown open) and should be replaced.
     
    Woody-202 and Shadetree Mechanic like this.
  10. Mark A Bradley

    Joined:
    Mar 22, 2019
    Messages:
    25
    Likes Received:
    11
    Hey,THANK YOU BUD, for the help,,I had a bad D20, ( replaced )and no juice at R103,,So I replace R103, R104,( Right next to 103 ), and replaced R51, next to the Transformer, I call this the KIT, when I get a bad R103 or 104,I replace all 3 or the higher voltage parts.Butt now,,I don't have a Red light now,,Green is bright as can be, ( no more pee yellow light ), so I shall get the schematics out and poke around. You know your stuff, want to be my friend,,,I am ever ones friend. If you get the awnser before I fix the red light, go ahead and let me know, post it. But I am going to seeif I can fix it before you post, Talk soon,,THANK YOU again, fart smeller,,,no smart feller,LOL
     
    kaos513 and Shadetree Mechanic like this.
  11. baconater4749

    baconater4749 New Member

    Joined:
    Nov 11, 2020
    Messages:
    6
    Likes Received:
    2
    I found the issue with the green light, the wire broke off the bulb,,everything was good,power through the wire,, ( OH, THIS IS ANOTHER RADIO,ANOTHER 29 LTD),soldered the wire back on the broken part off the bulb and now I have GREEN,,,Thanks again,,73's KB9GTB,,Mark
     
    sunbulls and Slowmover like this.
  12. sunbulls

    sunbulls Sr. Member

    Joined:
    Apr 25, 2017
    Messages:
    782
    Likes Received:
    1,345
    Great! It doesn't take much to break the leads on those LED's, especially if they were soldered poorly in the first place. I heat shrink over each each lead and I often use a dab of hot glue or a cable tie on the wires afterwards to help reduce that stress.
     
    Holydvr likes this.
  13. Mark A Bradley

    Joined:
    Mar 22, 2019
    Messages:
    25
    Likes Received:
    11
    Soldered and heat shrinked, I use the soldering iron to melt the shrink, don't get to close, you will melty the solder again, then OOP'S, start all over again. Have a good one,Thank's all, glad to work with ya all. 73's,,KB9GTB,,Mark
     

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!