Cobra 29 NW ST WX - weird problem

[CbRadiosPRONTO]

Difficult explanation...I'll briefly describe symptoms and skip to the weird stuff.

TX modulation drops to nothing after a few seconds of keying.
RX audio is faint, though the meter shows RX is working. Sounds like it's off frequency but isn't.
Turn on SoundTracker and it improves the RX audio but not the TX modulation.
ST red led bulb won't light up but bulb is ok.


Here is where it gets strange. If I press the SoundTracker button really slow, at some point, the light will light up red; and if I just hold it at that point carefully, it'll stay on and (ready for this?) all radio problems go away. As long as I press that button about half way in and hold it there so that red bulb stays lit, the radio transmits and receives perfectly. Replaced button w/ working one but it's not the problem. Also replaced channel/display boards.

 

[sonoma]

sounds like the sound tracker board is going out. have seen a simular problem like this a few years ago and removed the sound tracker here is bulletin if you want to try it.

http://downloads.cobra.com/CB/TSB/TSB10012.pdf

 

[CbRadiosPRONTO]

sounds like the sound tracker board is going out. have seen a simular problem like this a few years ago and removed the sound tracker here is bulletin if you want to try it.

http://downloads.cobra.com/CB/TSB/TSB10012.pdf

I think that deals with a different problem, however it's such a simple task that I will go ahead and remove the 2 caps and short the 2 legs of the ic and we what happens.

 

[sonoma]

I have had a ST board go bad and kill the radio, even a weather board do the same thing over the years. since you were messing with eh ST switch it felt like that could be your problem.

 

[CbRadiosPRONTO]

Well, this took care of part of my problem. After doing to mod, the radio transmits as it should. However, the receive still does not work properly. Everything comes in garbled,though the meter response as it should with respect to RX signal. Wonder how do bypass the entire ST in RX and RX. Or, should I steel a board from another ST (?)

 

[sonoma]

CB Pronto it has been so many years ago I do not remember just what I did to remove the complete board. you might call cobra and see if they can help to remove it from RX. I called them years ago and they sent me to their bulletins site to remove it. I remember playing around with parts and finally pulled it completely out and the radio started working as it should. hate to say it has been so long ago I just do not remember what all I pulled to fix the problem I had. all I know over the years I had the weather board go bad also and had to pull it out the same as the sound tracker board. not having a radio here with the board in it i can not remember what all I had to pull. I know I just looked at all the parts hooked to the board and removed what was hooked up with the RX also.
here is the link to all of cobras radio items. look and see if any helps you.

http://downloads.cobra.com/CB/CB.htm

 

[sonoma]

after thinking about your problem I am thinking you have a cap in the ST area that is going bad. if you have a signal tracer you could listen for the audio on the caps in the ST area and see if you can find where the audio is going bad on you. that is how I normally find bad caps in the areas of suspect. on the 29 radios I do not remember it having a seperate board as the others do. you have the radio in front of you so I believe it is built into the main board. the ST section just sticks out from the main board.