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Old 02-15-2014, 12:53 PM   #1
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Cobra 75 WX XT - Not Working

Need electronics repair help!

Love my Cobra CB -- had it for only about 2 years but it's now stone dead. I'm fairly certain that I left the power on after my last run and it stayed that way for a few weeks. If so, is there a way to check this and replace a simple burned-out component?

Any other ideas on why my handheld might be dead? I've checked connections between the handheld at the silver junction box and that's fine.

Thanks --


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Old 02-15-2014, 01:34 PM   #2
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I am sure that you have done some of this but I'll give you my steps to check the system out and pin down where the problem is.

1) Check that the interface box is getting power from your vehicle (battery electrical system where ever you tied in at)
2) Have you checked the pins on the cable coming out of the interface box to see if it is passing power up to the handheld portion
3) Does the handheld when power is applied make any sort of noise at all?
4) with the squelch knob turned all the way off do you hear static from the unit?
5) if you hear static is it faint with the volume all the way up or blasting you out of your jeep?

Those should tell you where the problem is. If its power to the unit power not getting to the hand held, if its a power up issue or display issue in the handheld and if the receiver is getting anything from the antenna. Lets you do a basic check on the critical points without trying to transmit.

Let me know what you find and I will help as best I can. I will have spotty internet access for the next 5 days but I will do what I can.

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Old 02-15-2014, 02:35 PM   #3
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3) Does the handheld when power is applied make any sort of noise at all? NO
4) with the squelch knob turned all the way off do you hear static from the unit? NO
5) if you hear static is it faint with the volume all the way up or blasting you out of your jeep? NO
Lunatic, some quick replies above. There is no sound or static or buzz or hiss; the handheld is dead as a doornail. I'm guessing either power from the battery or a blown fuse. I'm suspecting the latter, that's why I asked the original question. But I will try and confirm first the issue of power from the pins or a broken connection with the battery.

Tom
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Old 02-15-2014, 04:08 PM   #4
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Originally Posted by Lunatic_Fridge View Post

1) Check that the interface box is getting power from your vehicle (battery electrical system where ever you tied in at) SEE BELOW
2) Have you checked the pins on the cable coming out of the interface box to see if it is passing power up to the handheld portion SEE BELOW

Lunatic Fridge
OK I did as best as I could. First, I did not install this myself but paid the boys at ORW to do it.

Below is the battery photo. I don't see any elec leads that look like the one running to the junction box. I see the leads running to my winch and some cable bundles that look like they run to other parts of the car. Is it likely that the installer spliced the wire from the junction box into the middle of a wire and didn't run it all the way to the battery?



As for the connector from the junction box to the handheld, see below. There are five pinholes and, without knowing which one carried power and which one carried the return, I tried all possible combinations. Didn't get even a twitch on the DC voltmeter setting. And, yes, I calibrated and checked the voltmeter on the battery terminals and it read a strong 12 VDC.



By my logic, therefore, there is either something wrong at the junction box or the connection to the battery power (which is not visible) has shaken loose.

I wish there was an easy way to apply power to the disconnected handheld (would need to know the correct pins) just to prove that it wakes up and isn't the problem.

Lunatic, any thoughts?
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Old 02-15-2014, 04:36 PM   #5
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Looks like they wired it into the vehicle elsewhere. When you were using it before it died did you have to have the ignition switch on to use the radio or could you use it with it off?

To check for power at the disconnect put the negative lead of your voltmeter to the body or a known good ground (cigarette lighter socket outer shell maybe) and then check each pin. One should have power if power is getting to your interface box. I am agreeing that power is probably not getting there.

Without taking the jeep apart at this point I cant really give you any ideas on where to look for your fuse for the radio. Going to just have to start at that connector and trace the wiring back until you find it. Wish it were easier but sometimes its not.

You might also want to do a search on the internet and see if you can find a manual for that CB that has a schematic diagram. I know Cobra used it include one in the last few pages of their manuals for the older 148GTL's and 29 GTL's and Classics. Not sure of the 75 had one but its worth a few minutes to look. Then we can check it out to see which pins to power to light up the head itself and check it for current draw.

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Old 02-15-2014, 05:17 PM   #6
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OK.. so Cobra manuals are not what they used to be. I think I have one of these radios in the pile of parts I got with my Jeep. Let me get home and I'll see which pins they are so we can check out your radio. I should be able to do that by next weekend if you can wait that long.

Or if someone else has this model radio can you check out the interface box and post up which pins are for power?

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Old 02-16-2014, 02:41 PM   #7
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OK.. so Cobra manuals are not what they used to be. I think I have one of these radios in the pile of parts I got with my Jeep. Let me get home and I'll see which pins they are so we can check out your radio. I should be able to do that by next weekend if you can wait that long.

Or if someone else has this model radio can you check out the interface box and post up which pins are for power?

Lunatic Fridge
Lunatic, FYI -- I called ORW and they're going to take a quick look at the power supply issue tomorrow. The guy that does all the installs will be there.

But I'm still curious about the handheld itself so if you make some progress I'd be much appreciative.

By chance, would you also know which components to change to goose up the broadcast signal?
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Old 02-18-2014, 08:28 AM   #8
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Stand down Lunatic

Thanks for offering to help, and I think I've narrowed down the problem.

Took my rig to ORW so they can establish where they did the power connection. It wasn't to the battery and it wasn't to the fuse box.

Turns out they did the power tie in to the starter. That way, if the vehicle wasn't running, and I left the CB on, it wouldn't drain the battery. Fine.

After establishing that, we saw that the power line from the junction box to the starter was cut, accidentally but deliberately, by my mechanic. I'd asked him to remove an aftermarket alarm system a month ago that was dying and affecting my starter. I appears that my mechanic saw the additional wire, assumed it was part of the alarm system, and cut it as well.

Thanks for digging in and offering to help. You're a prince!
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Old 02-20-2014, 06:37 AM   #9
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Glad you got it figured out.

With the type of radio that you have. I wouldnt look to "goose" the signal any. This type of radio was meant to be useful in a limited capacity and take up no real space. Not to be out "shooting skip" or anything like that. Not to mention that it is illegal to do so. Might want to think about a different radio if you want to get into that game.

For me I just went and got my ham license when I wanted to talk further than a CB could take me. Now I talk around the world all nice and legal like whenever I feel like it.

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Old 02-21-2014, 10:19 AM   #10
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Might want to think about a different radio if you want to get into that game.

Lunatic Fridge
What kind of radio has better range than a CB? I'd like one with a range of a few miles so if I'm wheeling and my wife is back at the campground, a few miles away, I can contact her.

Or, something with greater range that might be better in emergencies.
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Old 02-21-2014, 10:30 AM   #11
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Your CB should be able to go a few miles back to the campground.

Lunatic is talking about amateur radio's.
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Old 02-21-2014, 11:27 AM   #12
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Well you can possibly get more range with just a different CB. The 75 wasnt meant to be a screamer and talk all over. It was designed for what it is, small and basically functional. Other CBs that are larger like the 29Classic or 148GTL take up more real estate in your Jeep but offer better receivers which will get you further by letting you hear more. In a CB with the power limits without doing something illegal you will want to look for a radio with a great receiver so you can hear fainter signals.

You will also want to look at your antenna system and make sure it is not the limiter in your system. Make sure you have as much of the metal in your vehicle bonded together to give you the best RF ground possible. This means your hood and tailgate being bonded to the body tub and the body tub grounded to the frame with wide braided straps. Once I get mine all set up for RF I can take some pictures for you on what I have done. Its going to take me a bit to do it thanks to all the work traveling that I am doing.

Also your antenna choice. Yes the 2 or 3 ft super flexible antennas are nice for out on the trail. They are a compromise, for giving you an antenna that will survive a rollover and normal trail rash you have an antenna that is not ideal for long range communications. To maximize your range you want something like a 102" stainless steel whip with a shock spring set up into a ball mount that is mounted into your body tub. Then a very low loss coax back to your radio. For my low band communications I usually use RG8 style coax. Yes this coax is a half inch in diameter. But when I want to talk around the world those better specs help. Yes it is harder to work with but with the ball mount and large whip you arent going to be putting it on a tire carrier or your tailgate so that loss of flexibility is not going to matter that much.

For me, if I am wanting to make a long distance contact I would get on one of my ham radios. This requires a license for every user and has some limitations depending on license class. The cost to get a license is a bit of time, some knowledge of electronics and radio, Rules, some basic math and I think its up to $12 for a test now. I am not certain of the testing cost right now, I upgraded to the top license a few years ago so I am not following the current rates.

To get started in ham radio check out the Amateur Radio Relay League for some good info and if you check in the Affiliated Clubs section you can find a local club to you and go meet some Hams. We are for the most part a friendly group and very willing to help folks join the hobby.

For ham radios you can get started with something as simple as a handheld one that will the help of a repeater you can get horizon to horizon coverage with a small radio that could be as inexpensive as a few hundred dollars with accessories. Or if you are looking for direct unassisted communications you can get a high power VHF mobile radio for a few hundred dollars each and wire them into your Jeep and camper. With antennas you would be looking at something around $300 each for complete installs in the Jeep or camper. For even more capability you could move up to a Dual band radio. This is a radio that includes a VHF section and a UHF section. Basically lets you access two different bands in one radio. This will give you access to more repeaters and spectrum that we can use to communicate. These radios start in the $350 range and go up from there depending on what you want it to do. You will also need an antenna that is a bit more expensive than a simple single band one but not that much more. I would expect to pay in the range of $120-150 for a good dual band antenna / mount setup for your Jeep and depending on what you want to do at the camper maybe up to $200 for the camper antenna system.

I know thats a lot to digest. I am happy to help with what I can, I have been in the Communications Industry for more than 20 years and in the Two Way Radio field for 18 years.

A radio hobby can be a lot of fun, and sometimes a big headache when things arent working right. But if you get your ham license and get on HF the first time you hear a voice come in over the static from the other side of the globe its amazing.

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Old 02-21-2014, 11:50 AM   #13
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Oh and for everyone that has a 75WX radio and wants to know if their power problems are in the handheld controller or the interface box/vehicle. You would want to connect power to pin 1 (+) and ground to pin 3 (-) to check and see if your radio powers up. On mine the pins are numbered in the handheld side of the connector. If not look for the alignment tab and start counting COUNTER clockwise to find the pins. So pin one is the first left of the alignment tab and pin 3 is directly across from it. Hope this helps someone.

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