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142 gtl help
- Thread starter kaos513
- Start date
D60 is reverse-polarity protection. Should not cause that symptom.
Do you have any transmit on sideband modes?
73
Do you have any transmit on sideband modes?
73
Kaos the protection diode is a 1n4003 and if it is still in line will read other components that are in line with it. it does not effect the modulation if that is the protect diode which I am taking it that is what it is since Nomad said it was. did not check the schematic. but that will not do any thing to your modulation.
Ok something went bad I recapped the radio aligned it and and was sitting on my bench for 2 weeks when I turned it on I lost modulation.
AM and sideband both?
Or just AM?
If it transmits on sideband, this means the problem is downstream from where the mike audio splits off to feed the SSB and AM modulators separately.
73
Or just AM?
If it transmits on sideband, this means the problem is downstream from where the mike audio splits off to feed the SSB and AM modulators separately.
73
kaos,
I want you to know that i don't mean any disrespect when i ask this, but do you ever look around for answers yourself before asking for them here?
The reason i ask is that we have been involved in many many radio repair threads with you, and it kinda seems like you aren't really learning anything from all the info provided to you because every time you buy another radio with a problem, you don't come here with a learned guess to build from, you just state the problem and hope someone has an easy answer for you.
please understand that those of us who enjoy helping with technical matters here on the forum (i can't speak for everyone obviously) do it in order to help teach someone to be able to fix their own problems.
That doesn't seem to be a goal for you, based on the threads in this forum.
for example, for you to wonder whether or not your reverse polarity diode would cause you to lose modulation when you are constantly working on radios and getting technical advice makes me wonder if the advice is just not clicking with you, or if you aren't bothering to try to learn anything from the people trying to help you, and would rather just be told, "take this part out and put that part in" type of answers.
can you see how that might get frustrating after a while for the advice givers?
imagine going to your buddy who knows about cars, and asking him why your car won't start, and he tells you to change the spark plugs, so you do it, but you never bother to learn why the spark plugs might cause your car not to start.
eventually this guy is going to get tired of telling you how to fix your car because you don't show any interest in learning about it.
i do hope this doesn't sound too harsh, heck i may be missing something obvious, but i must be honest that when i came across this thread, read the question, and then saw who asked it, i just kind of hung my head and said, "looks like kaos wants to be spoonfed an answer again".
so i guess the question becomes, am i wrong? i do hope that i am, and if i am, i apologize for asking these questions, and will continue to try to help your learning.
I'm asking because im confused, not because im angry or resentful or anything like that.
LC
I want you to know that i don't mean any disrespect when i ask this, but do you ever look around for answers yourself before asking for them here?
The reason i ask is that we have been involved in many many radio repair threads with you, and it kinda seems like you aren't really learning anything from all the info provided to you because every time you buy another radio with a problem, you don't come here with a learned guess to build from, you just state the problem and hope someone has an easy answer for you.
please understand that those of us who enjoy helping with technical matters here on the forum (i can't speak for everyone obviously) do it in order to help teach someone to be able to fix their own problems.
That doesn't seem to be a goal for you, based on the threads in this forum.
for example, for you to wonder whether or not your reverse polarity diode would cause you to lose modulation when you are constantly working on radios and getting technical advice makes me wonder if the advice is just not clicking with you, or if you aren't bothering to try to learn anything from the people trying to help you, and would rather just be told, "take this part out and put that part in" type of answers.
can you see how that might get frustrating after a while for the advice givers?
imagine going to your buddy who knows about cars, and asking him why your car won't start, and he tells you to change the spark plugs, so you do it, but you never bother to learn why the spark plugs might cause your car not to start.
eventually this guy is going to get tired of telling you how to fix your car because you don't show any interest in learning about it.
i do hope this doesn't sound too harsh, heck i may be missing something obvious, but i must be honest that when i came across this thread, read the question, and then saw who asked it, i just kind of hung my head and said, "looks like kaos wants to be spoonfed an answer again".
so i guess the question becomes, am i wrong? i do hope that i am, and if i am, i apologize for asking these questions, and will continue to try to help your learning.
I'm asking because im confused, not because im angry or resentful or anything like that.
LC
LC:
Thanks for answering exactly the same thing I was trying to put into words
kaos:
If you have a bad D60 that protects the 8v regulator; then perhaps you should wonder if the board still has 8v regulated voltage.
Think about it: D60 is the protection diode against reversed voltage. If it is shorted; what do you think will happen to that regulator? Sure, the diode fries. But what about all of the other 13v parts on the board - that are not on the 8v rail - that got a dose of reverse voltage that didn't have diode protection? Seems to me that it would be the right time to start checking voltages everywhere; don't you? Also ask yourself: what caused this problem in the first place?
There is also a service bulletin that deals with early regulator failure to put in once you get other stuff taken care of first:
http://www.cbtricks.com/radios/cobra/142gtl/graphics/cobra_142gtl_tech_note_1226.pdf
Thanks for answering exactly the same thing I was trying to put into words
kaos:
If you have a bad D60 that protects the 8v regulator; then perhaps you should wonder if the board still has 8v regulated voltage.
Think about it: D60 is the protection diode against reversed voltage. If it is shorted; what do you think will happen to that regulator? Sure, the diode fries. But what about all of the other 13v parts on the board - that are not on the 8v rail - that got a dose of reverse voltage that didn't have diode protection? Seems to me that it would be the right time to start checking voltages everywhere; don't you? Also ask yourself: what caused this problem in the first place?
There is also a service bulletin that deals with early regulator failure to put in once you get other stuff taken care of first:
http://www.cbtricks.com/radios/cobra/142gtl/graphics/cobra_142gtl_tech_note_1226.pdf
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I'm learning alot, this is a new problem and I never encounter before that is why I'm asking for help, as it was working before, no modulation on am and ssb.
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Guess what?
There is no simple answer for you!
If you don't do the work; then you can't fix it.
Re-read LC's post above.
What would I do? Well; I'd have to think about it. Guess the first thing I would do is to see if there is 8v on the pll. Why? Because the 8v regulator may have failed. If so; then I would have to replace the regulator, add an 18.2v zener diode, and another replacement diode at D60, as per the Service Bulletin #1226 describes/remedies.
Thinking about it some more, I guess that ALL of the devices that are hooked up to the 13.8v rail will also need to be tested. Let me think about that for a second Let's see: maybe the audio amp? Yes. Maybe the final? Yes. Maybe the AM Regulator? IIRC, yes. Other devices too? Yes.
Sooo; you have audio? Final output? Tested the AM Regulator?
But if you look at the schematic and trace all of the 13.8v rail devices - including diodes - they will all need to be tested. Thinking about it, either one of two scenarios happened. You either bypassed the built-in power supply and used the plug in the back and fed it reversed voltage - OR - the voltage regulator failed because it didn't have SB1#1226 installed. Better hope it is the latter.
Kaos,
i just got done typing up a long response, and then i re-read it and found it to be unjustly harsh, so all i want to say is this:
please start doing some reading outside of the forum, and not just on CB radios.
try reading some articles on how diodes work, transistors work, and how resonant circuits work just for a start.
that way you can come to the forum with a problem, tell everyone what you thought it was, what you tried, and why you thought it would help, instead of just stating the problem and hoping someone else solves it for you.
BTW, here is a 12 page thread you started on the same chassis with a similar issue last year. How much do you want to bet that the same information you are asking about now is contained in that thread?
https://www.worldwidedx.com/threads/uniden-washington.237276/
LC
i just got done typing up a long response, and then i re-read it and found it to be unjustly harsh, so all i want to say is this:
please start doing some reading outside of the forum, and not just on CB radios.
try reading some articles on how diodes work, transistors work, and how resonant circuits work just for a start.
that way you can come to the forum with a problem, tell everyone what you thought it was, what you tried, and why you thought it would help, instead of just stating the problem and hoping someone else solves it for you.
BTW, here is a 12 page thread you started on the same chassis with a similar issue last year. How much do you want to bet that the same information you are asking about now is contained in that thread?
https://www.worldwidedx.com/threads/uniden-washington.237276/
LC