hey Nomad one item you just mentioned brought back bad memories about living by a AM radio station. I use to live about 1/2 block from a station that put out 50,000 watts at daytime and 100.000 at night. you could listen to that station in your car about 500 miles away from it. the station would bleed all over your home phones and a cb that was not working properly would pick up the station like it was a AM radio. if you put a screw driver in your had and just got close to a radio it would scream like the volume was all the way up on the radio. sure glad I do not live there any more. that place made it hard to work on a radio and try to trouble shoot it.
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29 WX NW ST No TX and No RX; Need Help Please
- Thread starter BuckSkin
- Start date
Had a customer years ago who ran a taxicab company. Moved his base station to within a few blocks of an AM radio station tower. The cab drivers kept telling the dispatcher to "Turn down that radio so we can hear you. Its drowning you out". Frustrated the dispatcher, kept insisting there was no radio playing in the office.
Turned out that the phone line was carrying enough of the 1350 kHz AM signal into the room to bleed the amplified desk mike this Johnson base radio used.
Yeah, a power mike. On a business-dispatching base radio.
Moving the phone to the next desk cured the problem.
73
Turned out that the phone line was carrying enough of the 1350 kHz AM signal into the room to bleed the amplified desk mike this Johnson base radio used.
Yeah, a power mike. On a business-dispatching base radio.
Moving the phone to the next desk cured the problem.
73
Is the T1 a large (compared to everything else in there) approximately 1-1/2" square gizmo with a metal perimeter and what looks to be a wire-wound coil within, looking at the component side of the innards, with the face of the radio closest to me, this is on the right and beside the right-rear screw that is through the board; there is a T1 printed beside it ?
Where is the audio chip and it's pin 1; I am assuming it is a different component from the T1; does this audio chip have an identification ?
I found the D8.
When the radio was still in the truck and I was trying to diagnose it, the meter needle never moved regardless of what I did; however, I couldn't really say whether it may or may not have moved when the wife was attempting to talk to me from another truck; I will try and move my test antenna outside the shop and see what the needle does when she tries talking again.
I doubt I would get any signal at all inside this metal-sided building, even with a truck parked just right through the wall --- or would I ?
Thanks again for helping me.
You said that PA and weather audio work just fine.
Did they break since then?
If not, looking at T1 and the audio chip is a total waste of time. If you have PA and weather audio, those two parts are working just fine, and the problem is well upstream from those parts.
I suppose somebody should snap a picture of the two ceramic filters so you can try the "Manual Digital Signal Injector" test described above.
Just learning the names of the pieces in there, and what they look like is a good place to start before trying to test any of them.
73
Did they break since then?
If not, looking at T1 and the audio chip is a total waste of time. If you have PA and weather audio, those two parts are working just fine, and the problem is well upstream from those parts.
I suppose somebody should snap a picture of the two ceramic filters so you can try the "Manual Digital Signal Injector" test described above.
Just learning the names of the pieces in there, and what they look like is a good place to start before trying to test any of them.
73
nomad,
i took the "PA speaker works" to mean that he knows his PA speaker is good and is NOT the reason that he cant hear any audio out of it.
I could be wrong on that one.
as for the weather stations coming in, i think i just missed that one. LOL
i figured he said his speaker worked because he tried it in his other radio.
buckskin, listen to nomad, he is the man.
LC
i took the "PA speaker works" to mean that he knows his PA speaker is good and is NOT the reason that he cant hear any audio out of it.
I could be wrong on that one.
as for the weather stations coming in, i think i just missed that one. LOL
i figured he said his speaker worked because he tried it in his other radio.
buckskin, listen to nomad, he is the man.
LC
If I seemed to have ignored nomad's advice in my last posting, it was not intentional; for whatever reason, this site does not show me all posts as they arrive; I don't know what is up with that.
I have to refresh the page several times to see a new post and then earlier posts may not appear.
YES, some good clear pictures with bright florescent arrows pointing out the pieces I need to be poking my finger/screwdriver antenna into would be really helpful.
On that same line of thought, other than my radio having weather, are the internals and their labeling consistent with that of a 29LTD ?
As to the PA speaker: Yes, the PA speaker was working loud and clear when the radio in question was in the truck.
The weather is even working loud and clear inside this metal building and connected to an old magnet-mount antenna that is just sitting on the wood bench.
I appreciate you guys patience with my ignorance as I am truly a complete beginner in this radio fixing business.
I don't know of anyone in a hundred miles that tinkers with radios; all the ones that used to have been long buried.
I have to refresh the page several times to see a new post and then earlier posts may not appear.
YES, some good clear pictures with bright florescent arrows pointing out the pieces I need to be poking my finger/screwdriver antenna into would be really helpful.
On that same line of thought, other than my radio having weather, are the internals and their labeling consistent with that of a 29LTD ?
As to the PA speaker: Yes, the PA speaker was working loud and clear when the radio in question was in the truck.
The weather is even working loud and clear inside this metal building and connected to an old magnet-mount antenna that is just sitting on the wood bench.
I appreciate you guys patience with my ignorance as I am truly a complete beginner in this radio fixing business.
I don't know of anyone in a hundred miles that tinkers with radios; all the ones that used to have been long buried.
If there is nobody available to help nearby, you're stuck with being self-reliant.
What you need is a guide to troubleshooting without tools. Don't know anyone who has written that one, yet.
This is not a good week for me to undertake that task.
Closest thing to this are books written by a guy named Lou Franklin. The tricky part is "How do I only learn what I need to for JUST this radio, without having to learn all the other stuff that's not broke inside this one?"
So there's the dilemma. If being self-reliant will be the long-term plan, starting with Lou Franklin's "Screwdriver Expert's Guide" is what I would recommend.
His web site is http://www.cbcintl.com/
This still leaves the questions of how to test a part that you think might be bad. Somewhere on this forum a member posted links to some YT vids showing how to test diodes and transistors with a multimeter. Not my favorite method, but if that's what you have, it's the only option.
And if the problem is a failed 3-legged transistor that's not sold anywhere nearby, this poses a different obstacle. Minimum order policies, shipping cost, etc.
This is the reason that anyone who asks about learning to work on a CB gets told to start with a pile of junk radios. They can serve as a source of parts not easily available nearby.
No easy answers to the question "How do I fix just THIS radio without having to learn how to fix broken radios first?"
73
What you need is a guide to troubleshooting without tools. Don't know anyone who has written that one, yet.
This is not a good week for me to undertake that task.
Closest thing to this are books written by a guy named Lou Franklin. The tricky part is "How do I only learn what I need to for JUST this radio, without having to learn all the other stuff that's not broke inside this one?"
So there's the dilemma. If being self-reliant will be the long-term plan, starting with Lou Franklin's "Screwdriver Expert's Guide" is what I would recommend.
His web site is http://www.cbcintl.com/
This still leaves the questions of how to test a part that you think might be bad. Somewhere on this forum a member posted links to some YT vids showing how to test diodes and transistors with a multimeter. Not my favorite method, but if that's what you have, it's the only option.
And if the problem is a failed 3-legged transistor that's not sold anywhere nearby, this poses a different obstacle. Minimum order policies, shipping cost, etc.
This is the reason that anyone who asks about learning to work on a CB gets told to start with a pile of junk radios. They can serve as a source of parts not easily available nearby.
No easy answers to the question "How do I fix just THIS radio without having to learn how to fix broken radios first?"
73
I am not in any particular hurry; I can wait a couple weeks for your publication.
Actually, I do have a pile of various disabled radios and also several working radios as well; I frequent classic car and truck swap meets and often will buy a whole big box that says "C.B.Stuff" for maybe five or ten dollars and there will be all sorts of goodies inside.
I have accumulated several Cobra 19 in various versions and all of them work.
The curious fact that I have learned is that the the two old 23-channel Midland CBs I have seem to be pretty much bullet-proof and will out-distance and outperform any of my Cobras; then, I am not knowledgeable enough to tell, but these two radios came in the same box lot and may have had every upgrade possible done to them.
My main three trucks have custom designed CB openings in the overhead console that were purpose built to fit a Cobra 29; which is my main reason for sticking with them.
In a pinch, I will zip-tie one of the other radios in there and use it until I can come up with another working Cobra 29.
I have one of the old Midland 23-channel radios equipped with a cigar-lighter cord and a magnet-mount antenna and I often use it in trucks I may have reason to drive that do not have a working radio; it works so well that I am tempted to mount it in my truck as my main radio.
One would think that, with all this pile of CB stuff, that I would know how to fix them; but, I am a complete novice and appreciate any and all help and advice I can get.
Thanks.
buckskin,
I misinterpreted a couple of your statements which led me to suspect T1.
I was wrong, and as nomad said, T1 is not your problem if you have PA function and can hear the weather stations.
since the one part that could have explained both of your problems is not the culprit, we need to back track a bit so that we don't have any future misunderstandings.
let's check the radio once more before we start unsoldering things.
first, you are going to need a working radio set up next to your broken radio so that we can see whether or not the broken radio is receiving signals or not.
so, set the broken radio up like this:
noise blanker and ANL OFF.
volume up all the way. (clockwise)
squelch down all the way (counter-clockwise)
RF gain up all the way.
meter switch in S/RF position.
known good microphone plugged in.
antenna connected.
set the working radio up near the broken radio, on the same channel, dynamike all the way up, antenna connected.
now key the working radio (or have a helper do it) and watch the needle on the S-meter on the broken radio.
did it move?
it should have moved over towards the far right side of the meter, and probably shake around a bit when talking into the working radio.
once we know what we are dealing with, we can tackle each problem separately.
LC
I misinterpreted a couple of your statements which led me to suspect T1.
I was wrong, and as nomad said, T1 is not your problem if you have PA function and can hear the weather stations.
since the one part that could have explained both of your problems is not the culprit, we need to back track a bit so that we don't have any future misunderstandings.
let's check the radio once more before we start unsoldering things.
first, you are going to need a working radio set up next to your broken radio so that we can see whether or not the broken radio is receiving signals or not.
so, set the broken radio up like this:
noise blanker and ANL OFF.
volume up all the way. (clockwise)
squelch down all the way (counter-clockwise)
RF gain up all the way.
meter switch in S/RF position.
known good microphone plugged in.
antenna connected.
set the working radio up near the broken radio, on the same channel, dynamike all the way up, antenna connected.
now key the working radio (or have a helper do it) and watch the needle on the S-meter on the broken radio.
did it move?
it should have moved over towards the far right side of the meter, and probably shake around a bit when talking into the working radio.
once we know what we are dealing with, we can tackle each problem separately.
LC
I will try to check this out sometime tomorrow and get back with my findings.
I like the instructions you provided as they are easy to follow and understand.
Thanks so much.
Okay, I used one of the working Cobra 19 radios connected to a 4-1/2-foot fiberglass Wilson Silverload antenna; the radios were side-by-side on the bench, maybe three inches between them; the antennas were about two foot apart.
I could not see any meter movement on the bad radio when keying the mike on the working radio.
However, when I talked into the working radio/mike, although the needle never moved, the meter's back-light very obviously dimmed; when I was not talking, it would immediately brighten; when I talked it dimmed; so there is a wee bit of signal acknowledgement.
While I was nosing around under the hood of the disabled radio, I found the date "April 2008" in two separate places.
I bought this radio new-in-box some time in 2014, six years after manufacture.
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buckskin, i know that you mentioned this already, but while you have this test setup still together, please confirm that the RX/TX light on your broken radio does or does not change color when you key the mic on it.
This is key to know.
when you said that the broken radio was not showing any indication of any signals getting in, you mentioned that the lights on the broken radio were dimming slightly when you were speaking into the good radio.
you were wondering if this was some sort of indication of the broken radio reacting to the signal.
most likely it is not.
did you have both radios connected to the same power supply?
most likely what you saw was the increased current drain on the power supply during modulation peaks was "sucking" current away from the broken radio, causing its lights to dim.
right now it sounds like you have a dead radio, and the reason your problem is hard to track down is because you are saying that the RX/TX light is changing color.
every bit of tech savvy that i have is telling me that you are mistaken about the RX/TX light and you have a dead radio that lights up, but nothing else works.
LC
This is key to know.
when you said that the broken radio was not showing any indication of any signals getting in, you mentioned that the lights on the broken radio were dimming slightly when you were speaking into the good radio.
you were wondering if this was some sort of indication of the broken radio reacting to the signal.
most likely it is not.
did you have both radios connected to the same power supply?
most likely what you saw was the increased current drain on the power supply during modulation peaks was "sucking" current away from the broken radio, causing its lights to dim.
right now it sounds like you have a dead radio, and the reason your problem is hard to track down is because you are saying that the RX/TX light is changing color.
every bit of tech savvy that i have is telling me that you are mistaken about the RX/TX light and you have a dead radio that lights up, but nothing else works.
LC
Thanks so much for helping me.
I have just now went into the shop and checked the RX/TX light again, just to be absolutely certain about it; that GREEN light is definitely turning to RED when I key the mike; release the mike key and it returns to green.
As for the meter light dimming, what you describe is probably what is occurring.
I have a group of 12-volt truck batteries that are all connected parallel and maintained by a float charger.
Located at two of my workbenches I have + and - terminals that are wired to these batteries.
I use these 12-volt sources for various electrical component testing and troubleshooting.
So, yes, both radios were connected to the same power source, at the same terminals.
And, in the sake of clarity, that green light most definitely turns to red when the mike is keyed.
LooseCannon,
I was thinking the same thing, I had never seen what Buckskin described, until today; yeah usually the radio will still key up, at least if the driver/final stage are good. (& the light is switching)
I was running my Cobra 29 LTD Classic on the bench, listening to skip rolling and then I noticed one of my locals cutting in and out, so I went to key up and let him know that maybe he was having an issue over there!
As it turns out I was the one having an issue, I noticed when the s-meter was not moving anymore! The light was changing from green to red, but no transmit!! no receive, I was like wtf! (also, I still heard faint static when this happened, but no incoming signal)
Switched the radio off then on and the receiver came back (TX at the same time), after a little while the problem happened again, light was still switching green-to-red but the receiver was going dead and the radio wouldn't transmit, so maybe a mixing circuit?
I haven't looked it over yet, and i'm not proficient enough to "call it out" without actually looking around the radio and measuring something; but apparently this can happen, weirded me out for sure!
notes: my radio was manufactured in 1994, it is ready for capacitor replacement as they are all original. I could have a shoddy coax that has an intermittent connection. :/
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leapfrog thanks for the input. two people with similar issues helps rule out misinterpretations. maybe you can follow along with your broken radio and provide some perspective.
definitely a weird one, and something that i have not run across on a 29LTD, or if i have, i have forgotten what the heck was happening.
Buckskin, thanks for the clarification.
The bad news is, you have a problem that is going to be next to impossible (for me) to track down without having the radio in front of me (others may be able to do so, but i would need to test it myself).
however, in the interest of not leaving you in the lurch, and knowing that you would rather try something than do nothing; we can take a few random stabs at the problem and hope that we get lucky.
again, others may be able to help you more, so if you start seeing other advice to you in this thread, heed it.
ok, looking at the schematic, i might see a way that your radio can have no receive and no transmit, but still switch the LED. (this is a guess!)
check the voltages on TR23 in both receive and transmit. TR23 will be larger than the others on the board and looks about like the driver and final transistors.
post your findings.
next, unsolder all three legs of both the driver and final transistors and lift them off the PC board so they are not connected to anything, but are still bolted in place.
use this tutorial (or read some others) to learn how to test transistors using a DMM:
https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07
this will also show you how to test diodes, which you will also be doing.
both your driver and your final transistor will be leaded B-C-E with the transistor right side up and facing you, legs toward the ground.
check both of them using your meter, and post your findings.
now check C8. you don't have a capacitor tester, so the only test you can do is to remove it from the radio, and check it for a short. (it should read open)
if you can find another cap of the same value from another radio, you can switch it out to test it. (it is a 15 picofarad cap)
now use your diode check mode on your meter to check diodes D1, D2, and D3.
you will have to lift at least one leg out of circuit in order to test any of these parts.
post your findings on all of these tests.
a word of caution!
don't do two tests at once. resist the temptation to unsolder everything at once.
http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29ltdwx-st_29ltd_sch.pdf
http://www.cbtricks.com/radios/cobr..._st/graphics/29ltd-st_29wx-st_sm_pg1_pg11.pdf
http://www.cbtricks.com/radios/cobr...st/graphics/29ltd-st_29wx-st_sm_pg12_pg34.pdf
use these guides to help you.
good luck.
LC
definitely a weird one, and something that i have not run across on a 29LTD, or if i have, i have forgotten what the heck was happening.
Buckskin, thanks for the clarification.
The bad news is, you have a problem that is going to be next to impossible (for me) to track down without having the radio in front of me (others may be able to do so, but i would need to test it myself).
however, in the interest of not leaving you in the lurch, and knowing that you would rather try something than do nothing; we can take a few random stabs at the problem and hope that we get lucky.
again, others may be able to help you more, so if you start seeing other advice to you in this thread, heed it.
ok, looking at the schematic, i might see a way that your radio can have no receive and no transmit, but still switch the LED. (this is a guess!)
check the voltages on TR23 in both receive and transmit. TR23 will be larger than the others on the board and looks about like the driver and final transistors.
post your findings.
next, unsolder all three legs of both the driver and final transistors and lift them off the PC board so they are not connected to anything, but are still bolted in place.
use this tutorial (or read some others) to learn how to test transistors using a DMM:
https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07
this will also show you how to test diodes, which you will also be doing.
both your driver and your final transistor will be leaded B-C-E with the transistor right side up and facing you, legs toward the ground.
check both of them using your meter, and post your findings.
now check C8. you don't have a capacitor tester, so the only test you can do is to remove it from the radio, and check it for a short. (it should read open)
if you can find another cap of the same value from another radio, you can switch it out to test it. (it is a 15 picofarad cap)
now use your diode check mode on your meter to check diodes D1, D2, and D3.
you will have to lift at least one leg out of circuit in order to test any of these parts.
post your findings on all of these tests.
a word of caution!
don't do two tests at once. resist the temptation to unsolder everything at once.
http://www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29ltdwx-st_29ltd_sch.pdf
http://www.cbtricks.com/radios/cobr..._st/graphics/29ltd-st_29wx-st_sm_pg1_pg11.pdf
http://www.cbtricks.com/radios/cobr...st/graphics/29ltd-st_29wx-st_sm_pg12_pg34.pdf
use these guides to help you.
good luck.
LC
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