Cobra 29LTD Classic RX seems to go off frequency. Transmit is fine, but can't receive on same channel. i.e. TX on Ch 11, but RX some other frequency. Was talking to my wife and suddenly, her signal was gone. Was still receiving, but she was coming in as bleed over and I couldn't find the signal on any of the 40 channels. What could cause this?

First, you have to replace the cable as you will need a minimum of 4 wires, 2 of them for the transmit and receive switching, and a shielded cable for the audio. It would be nice to have another as the common for the TX/RX switching but the shield is commonly used for this.

You will need to re-wire the switch in the candlestick to allow switching from RX to TX.

Google "D104 to cobra 29 mic wiring" and you will find many hits for this.
Your microphone was not intended to work with this style of radio. To save a buck, the CB manufacturers removed a 50 cent relay to do the transmit/receive switching. You can see what happens when you remove the microphone when you are listening to the Cobra. It'll stop producing any sound. This won't happen with the Tram,

Also, you may have problems with the microphone as it is high impedance as indicated by no transformer or preamp in the base of the microphone. This may be a problem as the Cobra has a relatively low impedance input.

It might not seem obvious but on many, if not all, current CB radios have separate wires coming from the microphone for RX and TX. It seems like the mic wire for TRANSMIT may be open. It is a common failure.

For direct frequency input: i.e 2061.4khz transmit - (TX), (2), (0), (6), (1), (4), (ENT) - use (RX) for receive frequency.
For ITU channels - (CH), (4), (1), (2), (ENT)
Direct frequency inputs are restricted to authorized marine band frequencies.

Rx is an abbreviation for receive. (Tx is transmit) There are a variety of reasons a radio will be "stuck" in Rx:
1) Another radio in the group is stuck in transmit and you cannot reply if your radio is receiving the other radios transmission.
2) Your radio is programmed for Rx only.
3) Your radio has a Tx problem such as a bad mic, or something covering the mic opening.
4) Your battery is low or bad. It takes more energy to Tx than to Rx.

Best regards.

is it a total no TX. or just not getting out very far.?
could have a broken mic wire. or the CB / PA switch may be in a wierd spot try moving it.. are you getting the Correct RX frequency on the channels.. ie are you getting channel 20 on acutal ch 20. and if you switch to ch. 6 are you getting ch 6? if you could explain more..

look at a schematic of a 29ltd to do that.. the 25 does'nt have it in there easily.. the 29 can be fixed to change tx/rx freq. with the delta tune

Did you have someone get on channel 2 to see??? Maybe channel 2 was quiet and channel one had better receive or noise.. You never know until you check it with another radio. That is NOT a common issue at all on those radios. Better off doing that test.
"WILDCAT" IN LAURELVILLE OHIO
35 YEARS OF CB FUN!!!

Hello there
Here is the diagram for you
Cobra 29LTD, 29LTD ST, 29WX ST
Documentation Project
CBTricks.com
TIPS:
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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

Hi and welcome to FixYa,

Based on your description, a possible drift in the local oscillator.  Check the 10.24Mhz crystal filter and its local oscillator for output and consistency.

Good luck and thank you for asking FixYa.

1 why would you change the finals?? Have you checked you antenna? How are your SWR's? Crappy antenna's cause a lot of problems.

Use an external meter to see what the SWR is, and see what the output is PEP. If its low, then there is something wrong. If it is High, change the mic and turn up the dynamic all the way.

Next. Have you been messing around in there?? Tryin to get more wattage? You turned VR4? If you thought you were turning it up by turning it all the way to the right, you turned it all the way down. Turn it all the way to the left.