I have a cobra 29ltd crome had echo board installed works good till i trun my la 900 on get feed back or squilling how do i fix

Hi I have a cobra 29ltd crome I can receive but when I key the mic to talk like it use to before in the talk back and the needle doesn't move with I talk in the mic.

is there talk back installed? if so its probably too loud. You are getting feed back. The talk back should be low, just enough to hear it to check echo. 470 ohm resistor is perfect.

Hello there
Here is the diagram for you
Cobra 29LTD, 29LTD ST, 29WX ST
Documentation Project
CBTricks.com
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29LTD ST Owners Manual
29WX ST Owners Manual
DIAGRAMS
29LTD ST Schematic Diagram
29LTD ST Schematic Diagram
29WX ST Schematic Diagram
WX Schematic Diagram
29LTD, 29LTD ST, 29WX ST Factory Service Manual
Page 1 to 11
Page 12 to 34
29LTD Factory Service Manual
29LTD
29LTD Schematic Diagram
29LTD Schematic Diagram
29 LTD Classic Schematic Diagram (Courtesy of Rick Jackson)



Mic Wiring
Stock
1- Shield
2- Audio
3- Transmit
4- Receive
Astatic (4 wire)
1- Shield
2- White
3- Red
4- Black

Astatic (6 wire)
1- Shield & Blue
2- White
3- Red
4- Black
Yellow NC
Daiwa EM-500
Cobra CA Series
1- Shield & Black
2- Red
3- White
4- Blue
Galaxy DC-521S (4 wire)
1- Shield
2- Yellow
3- Red
4- Black
Galaxy CB-660EI
1- Shield & Black
2- White
3- Red
4- Blue
Sadelta
1- Shield
2- White
3- Brown
4- Green
Turner
1- Shield & Red
2- White
3- Blue
4- Black
Yellow NC

Turn off the talk back, make sure the echo is not too much, back the mic gain a bit.

Make sure the antenna has a good clean ground. I know it sounds silly, but here's what's happening: You're getting RF feedback. If you don't have a good ground at the antenna, some of the RF travels back down the coax and makes the whole radio "hot". Some of that RF couples back into the microphone input, and causes feedback.

It's also possible that if your amp is really big, you're getting RF feedback directly from the antenna itself due to the really strong field.

You could try moving the antenna further away from the radio, or if that's not practical, some snap on ferrite chokes (available at radio shack) around the mic cable near where it enters the radio will probably solve the problem.

This is a classic indication of a lost shield or ground connection in the mic circuitry. Double check these connections for good contact in the mic *and* the plug at the other end of the cable.

Check the grounding and SWR or "match"of the antenna system, too. A poor SWR (greater than 1.5:1 or 2.0:1) can cause the reflection of RF back to the radio. Modifications can increase sensitivity of the mic to this unwanted RF.

There should have been instructions that came with your reverb board. You are going to need to drill another hole in the case of the radio, or find a control where you can install a dual control knob onto.

Your reverb board is likely going to need 8v, so you will need to locate that off the logic board, likely from the frequency synthesizer. The the audio lines from the mic, or the output of mic amp, are going to be redirected to the reverb, and the output of the reverb feed back to where the wires were removed from.

If I recall correctly, the 148 is a bit of a bear to work with, not much room inside. You will likely have to get creative in placement of the reverb board itself. Make sure to wrap well so that it doesn't get tossed around and break something inside.

Hi and welcome to FixYa,

Pls click on the schematic diagram for a Cobra 29LTD.

Good luck and Thank you for using FixYa. Happy Holidays.

Hi there!!

If you have an echo board what kind is it? I can give you the connections and where they go it just depends on which echo board you have!! I can also tell you where that talkback goes!! Let me know

Dennis

Assuming you have a good SWR, either ditch the power mike or the truck.