Cobra 29ltd classic ( Rick, Please Help )

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pitbikeman
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Cobra 29ltd classic ( Rick, Please Help )

Post by pitbikeman »

Hi folks, the name here is Hawk

I just got a used cobra 29ltd classic (and I'm trying to find out what is wrong with it. Ok, some info on the model:
-Manufactured October 00
-Main board has this stamped on it: KEPC-060H, A068A-5
-I belive the main chip is this one: NPC D2816C

-Radio does transmit and recieve. I used an old flashlight bulb as a dummy load and the modulation makes the bulb go from fairly bright to extremely bright when saying "ahhhhhhh-deeee-ooooo".

-Recieve is having problems, I get plenty of static/noise in the speaker but don't hear anyone talking on any channel (no reply also when asking for radio check).

I'd love to have a few pictures of the internals to compare to mine because it's missing some parts and was modded by the previous owner. :shock: Some pictures of the bottom of the board would be good for comparison too because there's some resistors and stuff installed there... The biggest problem I'm having is a a buzz (feedback?) that comes through the speaker on receive about every 10 seconds (on every channel). It makes the meter move when it happens also. The poor cobra is more like a garden snake right now... it's missing capacitors C53 and C61 ( I would gratefully appreciate info on the values of those capacitors). Someone also snipped one end of Resistor R55 for some reason. Someone installed a "variable turbo mod" at location JP36 but I removed it and replaced it with a jumper to see if the strange buzz/tone would stop. I'd really like to learn about cb radio repair and put this radio back to stock. I have a mitral valve problem with my heart and I don't work so I have plenty of time on my hands. Also, transistor c2078 has a plastic bushing on the screw to keep the transistor from grounding to the heat sink, are the others that are mounted with screws supposed to have bushings too?

:D If needed, I do have a digital volt meter, and soldering experience.

73's
Hawk
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Rick
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Re: Cobra 29ltd classic no RX/TX

Post by Rick »

C53 1nF or .001uf, C61 100pF, R55 1K ? Watt. Replace there components and let us know how you get on.
Last edited by Rick on Sunday 9th Dec 2007, 8:06, edited 1 time in total.
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Re: Cobra 29ltd classic no RX/TX

Post by pitbikeman »

Rick wrote:C63 1nF or .001uf, C61 100pF, R55 1K ? Watt. Replace there components and let us know how you get on.
Nice to meet you Rick. I'm guessing you meant c53 but I'll go back and mess with c63 if need be. I replaced the components and think I got a slight improvement. It's still occuring about every 10 seconds. It kinda sounds like buzzzz-ummmp or annnnnt-unk, LoL... bare with me as I know it's hard to describe sounds with text. It's worse on some channels than others. I did some poking around and noticed that R104 and R103 gets pretty darn warm when in tx but the resistor has not discolored at all (too warm to keep your finger on after a few seconds). Anyhow, if need be I can film a short video of the goofy noise the radio is making and email it to you if that would help or take photos of the entire radio at your request. Appreciate your help.
Hawk
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Post by pitbikeman »

More info...

Did some more testing, unsoldered one leg on R104 and R103 to test them out of circuit. They are fine, R104 being 15.2ohms and R103 being 201.9 ohms. I figured, why not take some readings on nearby TR23(D880-Y) while I was at it. TR23 base is 8.4V, Collector is 14.2V, Emitter is 7.81V.

Don't know if this extra info will help or not but I figure I'll collect as much data as possible to send ya.

Hawk
Last edited by pitbikeman on Sunday 9th Dec 2007, 8:14, edited 1 time in total.
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Rick
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Re: Cobra 29ltd classic no RX/TX

Post by Rick »

R103 and R104 will run hot this is normal. Is the radio on frequency in TX? and can you hear any one?
TR23 is the main 8 volt regulator, and voltages you have given are ok.
Last edited by Rick on Sunday 9th Dec 2007, 8:23, edited 1 time in total.
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Re: Cobra 29ltd classic no RX/TX

Post by pitbikeman »

Rick wrote:R103 and R104 will run hot this is normal. Is the radio on frequency in TX? and can you hear any one?
TR23 is the main 8 volt regulator, and voltages you have given are ok.
Hi Rick, glad to see you online right now...

I assume the radio is on freq (don't have a freq counter) because I just heard a guy down the street barely and he gave me a radio check and said I was clear. This is good news but that horrible interference noise still persists.
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Re: Cobra 29ltd classic low RX audio.

Post by Rick »

Disconnect the antenna and switch off any PC in the house, is the noise still there?
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Re: Cobra 29ltd classic low RX audio.

Post by pitbikeman »

Rick wrote:Disconnect the antenna and switch off any PC in the house, is the noise still there?
No, radio goes quiet no sound at all from speaker with antenna disconnected
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Post by ramblingman »

hello,,,is the anl/nb helping at all when switched on..id bet,if this radios been modded much,this switch has been disconnected.to hook up talkback/noise toy or something like this in the past..and your running with no noise reduction.in turn it is picking up interferance from pc or other electrical devices in or close to your house.............ramblingman
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Post by pitbikeman »

Thanks guys, All is good, Rick found the source of the RFI.... as strange as it was.
Respect goes out to the guru, thanks again. :D
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