Question about Cobra 148 GTL 120-Channels Base CB Radio

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No am power

I have a Cobra 148 that works fine on USB and LSB but has no TX power on AM. Please help.

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  • Anonymous Oct 27, 2008

    I have the same problem. Radio has been T&P. Sat around for a few years, now AM does nothing. Will replace the AM regulator as you suggest and report back. Thanks!



    Michael

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  • 204 Answers

Radio dude, What you have is a blown am regulator. The sideband side does not use the mentioned transistor. They use a few different numbers here for the am regulator. One of them is a 2sc1419. On the Uniden Grant they put the transistor on the rear right above the antenna jack. On the 148 they put the transistor back in the right rear of the radio as your looking inside on the speaker side. Fixing it includes unsoldering the transistor and purchasing a replacement and resoldering it back in. This transistor is bolted to the side rail in the rear. I usually use a ECG152 as a replacement. It's not unusual to blow this one if the radio has been tuned. Let me know if your comfortable swapping it out. Otherwise it needs to go to a shop with a decent tech that won't take you to the cleaners. Let me know,, Mechanic

Posted on Feb 21, 2008

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I have an cobra 148 gtl no transmit


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Check first your microphone

• check if TX is engaging when PTT is pushed.


• check for continuity ( mic and cable )



If you have not done these steps,

try it first, or borrow other compatible mic for Cobra 148GTL

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Jul 28, 2012 | Cobra 148 GTL 120-Channels Base CB Radio

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clipping the limiter should not have prevented tx on sideband are u sure u didn't do something more accidently. r 131 is the correct limiter for the 148. just out of curiosity what year 148 is it?

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Jun 13, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Cobra 148GTL can't TX on USB


Its the cap that feeds the first transistor to the first of the finals. It is either shorted or burned out.

Or the audio IC. It could be putting just enough out on AM to seem like its working, and then not enough for side band.

look at the caps near the finals. Look for a burn one, or one that could be twisted, or shorted in any way.

May 01, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

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Hi Mate, the problem you are having in not uncommon in the
COBERA 148 GTL. I suspect that the problem lies in low value uF electro caps drying out (electrolite) causing power down and frequency drift. The capacitors are in two forms..tiny blue tantalum, and standard radial base caps that are grey aluminium
cans with a black stripe,it would be a job for a skilled person in electronics to replace all of them. The square metal cans with a screw ferrite slug are what you use to tune the radio, and as there are lot of them ,and you don't have a circuit diagram ,it would be pot luck finding the right one/s. What you realy need to know is all electronic devices age and hence, no longer do their job.
it would cost more than the set is worth to rebuild it,but if you have the skills ,it can be done. am cb with usb / lsb are a thing of the past now and you would be better off buying a used set that is still in top working order. The uhf sets are useless as was the am sets depending on what you want the sets to do, in convoy.... great....in remote country....useless. Having said that the am/usb/lsb sets are the best of the three because on ssb they tx on about 12 watts rms so you have a better chance of making contact, but don't count on it as hf cb is no longer in
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GOOD LUCK flyingfox@people.net.au

Jun 22, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Cobra 148 gtl new model


Hello bluzfan, Do you remember the old 40 channel CBs? they used basic A3A transmission (dual sideband single carrier)remember how you got crosstalk sometimes, if your power was too high? Then they went to 80 channel CBs (using a single side band as Lower Side Band (lsb) and the other as the upper side band (usb))? more crosstalk but they invented anl (automatic noise limiter)circuitry to compensate. Now you have the 120 channel CB which uses a form of side band multiplexing (20QAM) to generate 3 times more channel density 40 X 3 = 120. Here is my problem; Cobra should not have done this because you will have massive crosstalk and unaudible sounds because of the increase in channels but not an increase in initial (physical)bandwidth. I hate to tell you this but the only cure for the is to use it in 40 channel or 80 channel mode forget the 120 channel mode, or get a radio with better channel separation.

Oct 07, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Cobra 148 gtl


Open the radio up and find the L22 Can/Pot. It's the one with the wire soldered on top. With both fine and coarse Claifier/Voice Locks in the 12 O'Clock positions, confirm, then listen for someone that is on the correct frequency and turn this pot (small ferrite core inside) with a small plastic preferred screwdriver, until they sound clear. Do this for USB as well except, the Can/Pot is L59. Don't adjust the VR5 (transmit) unless you need to.

Oct 06, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

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