Cobra 29 RX problems

[iceman78]

Hello.

I found an old 29 project radio I messed with a while back. Everything works well except the receive.

I get some static (until I flip the ANL, then it does silent). I barely heard a local who normally buries my meter. The RF Gain doesn't seem to do anything either.

Here's what I tried:
Aligning the radio
Replaced TR7
Replaced R31
My audio (and PA function) are fine so I know the audio IC is operating.
Mic & wiring checks out ok

Nothing helped. I know I must be overlooking something. Any suggestions would be appreciated. Thanks

 

[iceman78]

Wow, what an overwhelming response! The problem was D3; replaced and RX returned as well as the RF Gain functioning.

I post this in case someone else has this problem in the future.

 

[OXSpanky]

What is D3? I am having basically the same issue. No to very faint receive - and I can hear the Weather channels bleed over if I hold my ear up to the speaker. RF Gain does nothing and I have verified Audio IC and speaker are working properly through talkback.

 

[iceman78]

What is D3? I am having basically the same issue. No to very faint receive - and I can hear the Weather channels bleed over if I hold my ear up to the speaker. RF Gain does nothing and I have verified Audio IC and speaker are working properly through talkback.

Pretty much the same problem i was having. Check D2 and D3 with your diode tester snd make sure they arent blown.

 

[OXSpanky]

Pretty much the same problem i was having. Check D2 and D3 with your diode tester snd make sure they arent blown.

Awesome - in the sense I have something to go on. This is a 29LX that is literally like two weeks old, brand new out of the box. I tuned the SWR properly and hardly used it - it's just been mounted ready for an upcoming trip.

I noticed I had a loose wire in my mic so I fixed that, and all of a sudden, I got no receive. I'll check them tonite - hopefully I can get new ones at Radio Shack if they are bad.

Thanks for the tips - I will be sure to let you know what I find.

 

[OXSpanky]

I swapped out D1 D2 and D3. they were all giving readings going both ways on my meter. still have the same issue.

Anyone have any direction they can point me?

 

[iceman78]

heck out the mic and the mic wires too. Also confirm the audio ic is working properly. put the radio in PA mode and plug an external speaker into the PA jack. if it works (which it most likely would) then the audio IC is alright.

You can also check TR-7 and D5 & D6. If that doesn't help then it's possible there's a bad cap somewhere.

I had a brand new 29 Black Chrome. Also had a very quiet receive. I had it aligned and the RX came back. So you may also care to look down that road as well.

I have heard some people mentioning that the new Cobra's are unusually quiet. Not that the RX is not working, just that they are quiet. But if you say the rf gain does nothing...it should be. Especially with a brand new radio.

Hope this helps a bit!

 

[OXSpanky]

heck out the mic and the mic wires too. Also confirm the audio ic is working properly. put the radio in PA mode and plug an external speaker into the PA jack. if it works (which it most likely would) then the audio IC is alright.

You can also check TR-7 and D5 & D6. If that doesn't help then it's possible there's a bad cap somewhere.

I had a brand new 29 Black Chrome. Also had a very quiet receive. I had it aligned and the RX came back. So you may also care to look down that road as well.

I have heard some people mentioning that the new Cobra's are unusually quiet. Not that the RX is not working, just that they are quiet. But if you say the rf gain does nothing...it should be. Especially with a brand new radio.

Hope this helps a bit!

Thanks for the advice - I'll see what happens.

I did check the audio IC via the method you outlined - checks good. I checked all mic wires and the connections at the jack, both look good as well.

I visually checked and did not see a bad cap visually, but I assumed there may be one that is bad. All of the solder joints look good and pressing the solder side while powering the radio didn't yield any different results.

I wouldn't say i have low recieve - i have none. The only thing coming through on the speaker, very faintly, in CB mode is the weather band. It's very faint and a bit garbled and the meter doesn't move at all.

I did have the radio aligned when purchased.

 

[OXSpanky]

Swapped mic with a known good one - Same issue. Put my mic on a good radio - works good.

Checked D5 and D6, they looked good.

I probed around the leads on TR7 but not sure what voltages I should be getting. Can anyone give me those values?

 

[iceman78]

Swapped mic with a known good one - Same issue. Put my mic on a good radio - works good.

Checked D5 and D6, they looked good.

I probed around the leads on TR7 but not sure what voltages I should be getting. Can anyone give me those values?

You can get the values on cbtricks. They have the service manual posted. It has the voltage table in there

 

[OXSpanky]

Awesome - Thanks!

 

[OXSpanky]

No go.

Contacting Cobra for Warranty service.

 

[iceman78]

No go.

Contacting Cobra for Warranty service.

Sorry you could't get it working. If it's a new radio they should warranty it.

Had a friend tell me that if you have a Cobra radio regardless of condition that has a problem, you can send it to Cobra and send them $40 or so and they will give you a new (or perhaps factory refurb) radio.

 

[OXSpanky]

Sorry you could't get it working. If it's a new radio they should warranty it.

Had a friend tell me that if you have a Cobra radio regardless of condition that has a problem, you can send it to Cobra and send them $40 or so and they will give you a new (or perhaps factory refurb) radio.

Interesting and good to know. I just got back from vacation and shipped the unit back to Cobra for a warranty repair - the tracking info shows they got it yesterday.

 

[OXSpanky]

Just got the radio back from Cobra 29. They only stated they found some open components - didn't say what. I do see some solder work on the board to drive the new face, but didn't look closer to see what they may have done.

Now can anyone recommend any mods?