Cobra 29 nw ltd classic, no receive.

[sonoma]

check the electro caps at the audio IC especially c48. it feeds the audio to the transformer and have found a few that were bad in that area. C48 has been the worst one to be bad.

also check for bad solder joints at the audio IC and there should be a surface mount cap on the solder side of the board at the IC. if it has lost its connection can cause this problem also.

 

[Ay589]

every one of the forums i read the steps where they say remove tr1, they figured their problems out but was other issues, i try to join to speak to them, but there is n registration on these forums etc so i have no way to even message the person reccomending removal of tr13, obviously they know the next steps

 

[sonoma]

do not be so sure they know. I have read them also and they get into what I just told you to check if they even give an answer. I had seen the same info you have read on cbtricks and they never went any farther than see if you get RX back when tr13 is pulled.

a couple guy's over there have you look for what I just gave you. in most cases this is where the problem is at.

 

[Ay589]

I have replaced every cap. C48 twice lol just because. That surface mount cap you speak of, is that the little ceramic going to ground on the chassis?

 

[loosecannon]

does the RX/TX light turn from green to red when you key the mic?
does it look like anything weird is happening to it when you key it or does it just go right from green to red?

i know its a weird question, but there is a method to my madness.
LC

 

[Ay589]

Ask as many questions, the more details we give eachother, the easier is is to narrow down the issue. Ok as for rx/tx lights, they are working as they should, it goes directly from green to red. And also, I mess with squelch and nothing changes, possibly disabled because of tr13 removed, but idk. Also Volume level at max is the equivilent to being normally on 1/4 way. And it crackles the whole time it's up there. My transmit voice is also low and very distorted. I'd start swapping diodes and the ceramic caps also but they're all so close together and so many that I don't wanna start opening an even bigger can of worms. The electrolytic caps I didn't mind changing every one because they're so easy to trace

 

[loosecannon]

sounds like you have a squelch problem. you most likely shorted out a transistor when your radio touched the pliers.

try replacing TR11, 12, and 13.

my guess right now is that the distorted TX audio is a separate issue caused by replacing the final, and that might be cured by re-tuning the transmitter once the radio is repaired.

if replacing TR11,12, and 13 doesn't get you anywhere, try replacing C36.

actually, try C36 first, then test the radio, then try the transistors.
LC

 

[Ay589]

I will get back to you as soon as i get out in the shop and try that!

 

[Robb]

I've done everything they're recommendinbesides remove each diode resisor capacitor and l test. Can't really test them on the board because resistance gets put throughout it right?



Still though. I read 3 places about "removing tr13 and if audio comes back " and they don't go any further on the subject. What's the next step from that, gotta be headed somewhere in the right direction. I replaced tr13 with new but no fix.

Did you actually test the TR13 transistor - once you took it out?
If not; then do so.

 

[Ay589]

I'm not sure how to test them. But I have donor radios with the same transistors and caps and I've put 6 different transistors in its place. Once you touch that one last leg to the board it goes silent. I followed the circuit as much as I could and swapped other caps resistors and some diodes with no improvement. I haven't made it worse which is great. But no better either lol

 

[Robb]

Difficult and nearly impossible to work on radios w/o basic equipment and knowledge of the components themselves. This isn't like replacing a bad spark plug wire on a 1970 ford truck; troubleshooting the receive circuit needs the right tools.

 

[Ay589]

I understand that. But I only have what I have. It's harder to find the issue without the proper tools, Having every tool in the book makes it easier yes but if I could get an understanding of this board, my many many donor parts and my good multimeter should get me by, just don't know how to test transistors etc and I believe my problem isn't only the receive circuit because the audio for transmit and receive are exactly the same, but I am new in here so I could be way wrong. Please don't take anything I say as smartalec or anything people would say my transmit is off! Lol,(I'm not the best with words), I don't want to come off rude at all . I want to learn

 

[loosecannon]

here is a great tutorial on how to test transistors with your multimeter:

LC

 

[sonoma]

you just said your TX audio and PA is the same. do you have a good audio IC to replace the one in this radio with. just saw it was caused by a short also. you may have blown the audio IC. I had a radio doing this last year and it was the ic bad. found out the radio had been shorted and was getting popping noises in PA and TX mode also.

 

[Ay589]

here is a great tutorial on how to test transistors with your multimeter:

LC

Thank you so much !!!!!!!