OK TAKE THE COAX OFF THE CB AND CHECK THE OUT SIDE AND INSIDE FOR CONTINUITY 0 OHMS IT IT DOES NOT SHOW 0 OHMS THE COAX IS GOOD. YOU ARE READING THE CIRCUIT INSID -E THE RADIO AND IS NORMAL.
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Mack's cophased harness just merges the two wires at the connector going to your radio. If the radio falls out of compartment and is caught by the coax it could damage this connection. Outer shield and inner lead could short here. I have replaced many a final due to bad coax for my company which primarily Mack. Well i say that but it is the beloved company driver that continues to talk on a bad antenna system. It actually take a while to kill a final even with out an antenna attached. Good Luck...........
B2470
Cellular Phone Antenna Circuit Malfunction
VCIM
DTC B2470
DTC B2470 04: Cellular Phone Antenna Circuit Malfunction Open Circuit
The cellular antenna is connected to the communication interface module (CIM) with a RG-58 coax cable. The CIM polls the data from the cellular antenna once every second.
Circuit/System Testing
Ignition OFF, disconnect the cellular antenna coax from the CIM module and the cellular antenna.
Ignition ON, test for less than 1 volt between the antenna coax center terminal and ground.
? If greater than the specified range, replace the antenna coax.
Ignition ON, test for less than 1 volt between the antenna coax outer shield and ground.
? If greater than the specified range, replace the antenna coax.
Test for infinite resistance between the antenna coax center terminal and ground.
? If less than the specified value, replace the antenna coax
Test for infinite resistance between the antenna coax outer shield and ground.
? If less than the specified value, replace the antenna coax
Test for less than 5 ohms at the cellular antenna coax center terminal from end to end.
? If greater than specified value, replace the cellular antenna coax cable.
Test for less than 5 ohms at the cellular antenna coax outer shield from end to end.
? If greater than specified value, replace the cellular antenna coax cable.
Test for infinite resistance between the antenna coax center terminal and the outer shield.
? If less than specified value, replace the cellular antenna coax cable.
If coax cable tests normal, replace the cellular antenna.
Clear the DTCs and operate the vehicle within the conditions for running the DTC. Verify DTC B2470 does not set.
? If the DTC sets, replace the CIM.
Have the radio tested first on a dummy load--if ok check the connector on the antenna--Big Stick antennas if old can break inside but a SWR check should reveal if a open antenna or a shorted one----you with a ohm meter should get a reading across the center pin to the threaded part of something like 50 ohms---either the antenna, coax or even the radio....
A VSWR meter is your best bet. They are cheap for cb's . If the antenna is badly mismatched you will get an antenna warning lamp on. If the antenna has a tuning coil you will see usually continuity to ground from the whip. Use the vswr meter on the radio. Set to calibrate first, transmit on channel twenty while rotating the swr cal knob. set needle on orange triangle at top right of scale. Select VSWR mode and transmit. needle should move up slightly if antenna is tuned correctly. Try chaneel 1 and 40 with same procedure. You can tell if antenna is tuned more toward the high or low frequency by how high the needle is on the scale. The higher the reading the worse the match is. If there is always a high scale reading then try another antenna that you know works.Watch for flattened/damaged/water in between braid and jacket or corrosion on coax as this will change the coax impedance drastically
The most important part of a CB set up is the antenna and the coax/connectors being used. Make sure your antenna is a good one. If you want a suggestion on a good one leave a comment with your budget and weather your using a mobile/base set up. Make sure your connection is goo. Check the PL259 and make sure the braids have not split off for inside. Soldier a new one on if necessary.
I will give you some instructions to peak your CB and adjust the receive. Make sure the CB ha no power and use a plastic screwdriver inside your radio.
Pull the bottom cover off of your radio.
Put a watt/power/SWR meter inline.
VR1 is your receive gain, adjust that to pick up from farther away. Note white noise can occur along with this as you will be sensitizing the front end.
Adjust VR4 for 100% modulation (swing)
Right by the final is a can with some glue on it. Scrape the glue off and turn that ferrite out until your power output is 4 watts RMS (not bird)
Your Cobra 29 is now peaked and tuned as much as possible without using a Oscilloscope. And doing this this way will not require a re-alignment afterward.
Don't touch any other pots in the radio.
If you have any comments please feel free to leave them here.
when mic is pressed transmitter is engaged. First is the Fuse the proper fuse? Could be an antenna-coax problem. Get a dummy load and hook up to your CB and try it again. If it doesn't blow the fuse, the problem is indeed in your coax antenna system. another way to test your antenna coax is to disconnect it from the radio, take a multimeter, set it to ohms 200 ohm scale, put one lead on the center pin of the coax and the other on the outside of the connector on the coax.if it shows anything at all, you have a short and that will not work. It needs to not read anything. To be sure the antenna system is ok other than swr you can also check the coax an antenna for continuity. one lead of meter on the coax center pin then other on the antenna. should get a reading, a low value. again on the outside of the coax at the connector and at the antenna side on the outside of the coax connector. should be a low reading. but you cannot have a reading from the center of the coax to the outside of the coax. disconnect the coax at the antenna and measure from center to outside at the coax if the previous reading showed a value.If you see a value on the meter, any value, your coax has a short. not good. most likely at the coax connector. redo the connector. It is possible that the coax got compromised somehow and got smashed to the point the outside coax meets the inside and touches. Now the other possibily your fuse blows, kis because the final output transistor is bad. So if you hook up a dummy load to your radio and the fuse still blows, then the final transistor is bad. This is probably due to a bad coax-antenna system. So before you replace any parts check the coax-antenna system first or you will have the same problem and burn out another transistor in the final. If none of this helps then just get another radio or have a god buddy look at it that knows about radios. Trade him another radio or something to fix it.
Hi sqa, my name is John. Welcome to FixYa. First thing to do would be is check your antenna system. Check that it is grounded good, like to the body of vehicle, and that nothing is blocking it. Next, check the coax cable, you will need a ohm meter to do this. Put it on the OHM scale, then with one of the probes, touch the center wire of the coax connector, while touching the other probe to the outside of the connector. If you get any kind of reading on the meter, the coax has a SHORT in it. If not, then the next step would be to check the SWR on the antenna. You can get this done at any locale CB shop for free. Try all these steps and still no solution, let me know and I will be glad to help you. Thanks for choosing FixYa....John
Having that short a range would give me the indication that there is a disconnect in the antenna system. Here's a couple of clues: Is the connector on the back of the radio connected to the coaxial cable?
If it is not factory installed connector, is it possible that the solder job on that connector was bad? If the cable is old, it could have a crack in the coax.
Is it the RIGHT kind of coax? It should be an RG-8, and RG-58, or a variation of those types of cable. It would likely be marked with "50 Ohm" somewhere along it's length.
Is the connection at the antenna solid? A firestick antenna for CB looks like this:
You must make a good connection at the base of the antenna from the center coax conductor that does NOT short it to ground, and the ground conductor should attach to the antenna mount frame.
With your symptoms, it is very likely that either the center conductor has worked loose, has become unsoldered from the terminal lug, or your coax has come unsoldered from the center pin. All of these things would really honk up your SWR, or Standing Wave Ratio, which is sort of like a string on a guitar that is tuned to a specific frequency for a specific note. The center freq of the CB band is 27.155 Mhz, so you would typically "tune" your antenna for that to be the lowest. A firestick KW is not tunable, so that should not be an issue. Look to your coax at both ends, and the coax itself to find your problem. If you have a simple ohm meter it would help to locate the short circuit. Good luck, write back if you need some assistance in further troubleshooting.
you need to check the connectors on the coaxial cable that plugs into the radio and antenna with a resistance tester from the pin in the center to the outer case there should be a resistance of infinity any reading on the meter says there is a short circuit in the cable and u will not transmit make over the connectors on both ends of cable make sure the center and outer wires do not touch
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