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cobra 29 nw st wx no weather audio

keb

Member
Dec 5, 2022
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Any ideas on why i have no normal audio for the weather stations. If I turn on WX I can only hear the weather faintly with the volume all the way up, and if the sound tracker is on, I don't hear anything. Other than that everything functions as normal, all audio is loud and proud in cb mode and pa mode. I have replaced the caps on the small weather board, there were only 3, to no luck. I have replaced the ta7310p,tc4066bp,ta31101ap as well as the audio ta7222ap chip. I have also replaced Ic2, ta7310p, but that was for no transmit. any ideas will be welcome. thx
 

Its definitely a mind boggler for me, the weather station audio is so faint that you have put your ear to the radio to hear it. I don't have a low pass in line, just a wilson 5000. I was thinking of replacing some transistors Q703 and Q704 il945s, I have some NPN 945 transistors but they are smaller than the ones cobra used.
 
Considering you've changed a lot of parts, I'm not sure where to start.

Ok, the WX line comes from the small PCB board - it has the audio.

On your main board, you should have a transistor oddly labeled - like Q801 - from the RX audio side - it buffers and amplifies the detected audio - and the WX line arrives here to this line just to the base of Q801 (if it's labeled as such).

The WX function gets power from and sends power to the radio to power this transistor (in case of an alert for example) so it can send the audio that gets amplified at Q801 - into the audio chip.

It also has to pull Squelch low so it doesn't quench the WX info. So there is a line that "grounds" the squelch so it can open the WX to full volume.

But it has to "see" this audio - so something tells me you simply rewired the radio and missed the connection point the WX needs.

Or...

You didn't or are not sending the ground toggle line to the right transistor on the Squelch amp circuit (TR12?)
 
So the search is still going for the weak weather audio. I went ahead and replaced Q801,Q703 and Q704 to no success in solving this issue. I'm trying to understand why the full volume position I would say is at 10% audio and the connection between that and the sound tracker button, when sound tracker is activated the volume goes completely away, nothing. The radio is a 1997 model, maybe i should recap it and see what happens......
 
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Don't just replace, you need to check...then if bad - then replace.

The older radios - like what you have, if nothing has been done to them, many just need a little TLC and perhaps a new cap or two - as you've suggested.

The solid state parts then can work when the older caps that would not let power flow into them - finally get powered.

As you check - use a multitester to look for voltages and you can even use the test leads as small noise injectors to help isolate the problem.

As radios age, the soldering is one of the weakest points on the board. On top of the fact that much of the Pb lead free - means the solder used is not the same as the older malleable solder using Lead.

So the low audio just might be from older weak solder joints from the wires coming off these boards onto the main PCB - even the work they have done to help interface an older non-WX board to take on the WX boards - they need some rework in the traces to "balance out" the volume levels between RX and WX - this may be one of them that needs to be re-viewed and gone over to fix bad solder traces and components repositioned on their pads on the foil side to make the radio work again.

This is from PC-66/PC-68 comparisons for WX and DSC work they had changed their layouts...
1674351873538.png
PC68XLAudioVolumeSquelch.png


I hope this can help guide you - you'll need to take photos of the board before and after the changes so you can retrace your steps if needed.

Now, for the C29 - the WX board can be many things, up to and including a board a lot like Unidens 7 channel. Hmm - so your radio is a 1997 - so it may be a 3 or even 5 channel --- either way, just wanted to point out...

1674354133478.png

IF your radio works normally in CB side, but just has low audio on the WX side, the board also works the Squelch transistor TR12 - so if your audio drops - try grounding TR12's base - like they do here. See pin 3?

When you recap, look for WX control line (Pin 7) - it has to power the audio pipe that arrives from the WX channel selector thru a separate pin - pin 10.
 
Last edited:
Sorry for the long delay, life happens, but anyway I started to look into the weather circuit and with your insight that the output audio was point 10, I changed some more transistors related to the squelch and testing as I went to see if it would work, well the capacitor c702 was the culprit. So glad I found that, as I have 2 other cobra 29s wx with the same issue. Hopefully its the same issue!
 
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