Question about Cobra 148 GTL 120-Channels Base CB Radio

5 Answers

Cobra 148gtl no tx audio receive ok,tx carrier on am no modulation though mic just stopped.replaced ics ta7222p and voltage reg mb3756.maybe its in the mic amp any help please.

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5 Answers

Re: cobra 148gtl

Without having a look inside of radio. but sounds like the voltage req chip on the side of radio.i think off hand its mb3756 .yes just got out manuel this one .usually causes problems like your back.cheers from new zealand..rick.

Posted on Feb 20, 2008

Re: cobra 148gtl

Tomcat 1 back ...i have found the fault no modulation on am/usb/ -23 a bc458 transister .replaced this transister and wow modulation on all 3 modes thanks zeppfrog for telling me where to look .

Posted on Mar 01, 2007

Re: cobra 148gtl

Ok collector of tr-23 reads 1 volt with a dead key or without the dead key .the r-120 reads 6.5v with a dead key or without a dead key .i have replaced the capacitor 330uf to a 16v.replacing tr23 could be at fault.end of press for now i will get back..

Posted on Feb 25, 2007

Re: cobra 148gtl

Yes i remember some tec said sometimes people add a power mic and dont wire it right get modulation wire wrong and feedback .wrong wiring blows out the c18 electrolytic capacitor .thanks zeppfrog thanks for the help i will do some testing.i replaced the meter light and the tx light with the a cool blue led it looks smart.i will get back with the results.

Posted on Feb 23, 2007

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Re: cobra 148gtl

I am having this trouble as well. The ics was my thought too, but I think it is in the modulation circuit somewhere. another article i read said to check this. "Look for the collector of TR-23, you should read about 4.5 V with a dead key. If you find that this voltage is not present, check on the opposite side of R-120 for 6.5V. Most likely this voltage will not be present; if this is the case, C18 has shorted and needs to be replaced. This is a 330uf, 10V electrolytic capacitor beside L31. To prevent "future" problems, replace with a 16V unit." As of yet, i havent gotten that far. note this is from the cobra 2000, but they are very much alike. you might cross check the resistor capacitor numbers though. btw, isnt the mb3756 the pll ic?

Posted on Feb 15, 2007

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Good day I have an cobra 148 Gtl tx and rx a working but no out put

It might not seem obvious but on many, if not all, current CB radios have separate wires coming from the microphone for RX and TX. It seems like the mic wire for TRANSMIT may be open. It is a common failure.

Feb 28, 2015 | Cobra 148GTL

1 Answer

148 gtl cobra cb radio and the rx/tx light stay on

This sounds like a problem with the MB3756 Regulator IC. It controls voltage regulation and TX/RX Switching. It is a common failure in these radios. Check voltages with schematic that can be found at
CB Tricks Home Page

Sep 02, 2013 | Cobra 148 GTL 120-Channels Base CB Radio

2 Answers

Need Cobra 148GTL with Cobra HG M75 pin-out color code

1audio. 1red
2shield. 2shield
3receive. 3blue
4switching. 4white
5transmit. 5black

Hope this helps

Jul 03, 2012 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Radio quits after 15-30 seconds

without more detailed info, quick suggestion - thermal fault, if all TX audio works when in this fault condition, it may be fair to assume audio IC is ok and check electrolytic capacitors and dry joints.

Nov 28, 2011 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

No modulation with strong carrier

sounds like your Audio Output went out......not audio chip....may be your voltage regulator also....your voltage regulator IC is heat you have a schematic?

Jan 23, 2010 | Cobra CB Radios

1 Answer

Pro 640e

How are you testing the audio out?
Are you using another radio?
If so, are you REALLY sure the other radio is ok?
If the other radio is ok, how do you know the mic is ok? have you tested it with another radio?
If the mic is ok, id have a look at the mic socket to check that all the pins are still there. Then open the radio up and check the socket is still connected to the main board.

Let me know how you get on..

Feb 02, 2009 | CB Radios

1 Answer

No receive cobra 29 ltd classic

Hi and welcome to FixYa,

Initially, pls confirm that there is modulation (transmit audio). The reason I asked is if IC4 (TA7222P) is blown, then the radio would have no audio amplifier which would explain no receive audio. Additionally, the final and pre-final (TR15 & 15) gets is modulated TX+12 through D8 from T1 which in turn is the output of IC4 through C48.

Perhaps a schematic diagram may be of further help.

Good luck and Thank you for using FixYa. Happy Holidays.

Dec 18, 2008 | Cobra 29 LTD CB Radio

2 Answers

Not working

you have more than likely a dead audio output ic gone faulty.look into radio on its back you will see the audio ic on the upper righthand side of radio.the heatsink is bolted onto the case with a plastic screw . its in a single inline package type.

Jun 28, 2007 | Cobra 148 GTL 120-Channels Base CB Radio

3 Answers

142 GTL no sound

yeppers you have a common problem of the audio output IC being bad or a defective speaker. If there is an external speaker jack, try another speaker just to make sure. Good Luck

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

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