Question about Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

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

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  • 37 Answers

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

Posted on Nov 25, 2014

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4 Suggested Answers

6ya6ya

6ya staff

  • 2 Answers

SOURCE:

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Posted on Jan 02, 2017

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Anonymous

  • 27 Answers

SOURCE: Cobra 148 gtl Low / No receive audio

No audio out / low audio out....This is a constant problem with the COBRA 148 gtl....to get a good level of volume replace the
electro caps ...start around the two speaker wires and work back from there. I'm in the process of rebuilding a 148 gtl and have found caps that are leaky and dried out...after replacing nine the volume went up to a good level...now i need to fix the distortion
and background hash. Did you know that there are many posts
on FIXYA about this same problem I.E. great TX , great PA but poor , or no audio out. these sets have been made in sevetal countries...The sets made in Taiwan or China have poor quality
front panel pots (the carbon track is micro thin and simply wares through to the material the track is printed on) This has the same effect as removing a wire from a pot I.E. no audio. The good news is that 99% of parts in the radio are freely available and that includes the front panel controls. ONE WONDERS IF THE SET IS WORTH THE EFFORT !!!

CHEERS GUYS / GIRLS.

Posted on Jul 03, 2008

Ironfist109

Iron

  • 3018 Answers

SOURCE: schematic diagram of cobra 148 gtl cb radio china made

  • Locate the MB8719 chip that is right behind the channel selector. Wire a SPST switch from pin 10 to ground and another from pin 11 to pin 12.


  • Channel Chart
  • Position 1: sw1 down, sw2 down
  • NORMAL CHANNELS

  • Position 2: sw1 up, sw2 down
  • 15=26.815 20=26.885 25=26.925 30=26.985(ch3)
  • 16=26.835 21=26.895 26=26.945 31=26.995(ch3A)
  • 17=26.845 22=26.905 27=26.955 32=27.005(ch4)
  • 18=26.855 23=26.935 28=26.965(ch1)
  • 19=26.865 24=26.915 29=26.975(ch2)

  • Position 3: sw1 up, sw2 up

  • 1=27.605 6=27.505 10=27.555 14=27.605
  • 2=27.455 7=27.515 11=27.565 16=27.475
  • 3=27.465 8=27.535 12=27.585 20=27.525
  • 4=27.485 9=27.545 13=27.595 23=27.575
  • 5=27.495

  • Position 4: sw1 down, sw2 up

  • 1=27.605 11=27.725 21=27.855 31=27.955
  • 2=27.615 12=27.745 22=27.865 32=27.965
  • 3=27.625 13=27.755 23=27.895 33=27.975
  • 4=27.645 14=27.765 24=27.875 34=27.985

Posted on Nov 09, 2011

Ironfist109

Iron

  • 3018 Answers

SOURCE: cobra 148 gtlcobra 148 gtl DX

  • Hi, here is your users manual http://minus.com/m8geTULWN#1 just click "download" if you want a copy of it. I have a copy of the service manual as well. Let me know if you want a copy.

  • Hope this helps.

Posted on Nov 29, 2011

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1 Answer

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.

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five pin /4 pin? (white D-104?)
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Jan 03, 2014 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

My cobra148gtl will not transmit


First check voltage of IC 4 (mb 3756) pin #8 in TX mode should be 8.0 volts. Check the voltage of the center leg of Tr36 (Final) and of Tr38 (Driver) RX=13.78 volts DC, TX=4.5 to 6.5 volts..

Jan 06, 2011 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

When i key the radio it stays on rx does not tx


Sounds like you have a broken microphone wire or a bad mic switch.

Sep 12, 2010 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Its a mk1 148 i have just bought it and need to know how to colour wire a standard k40 mike in as in wich wires where.not much experience.a picture would be helpfull


no need colors. look at the switch and plug to verify them. on 4pin cobras/galaxy/connex radios
pin 1 ground
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1 Answer

148 cobra with no modulation


possably corrosion on the pins of the plug into the radio, unscrew, push in and out a couple of times, and try again, maybe a break in the cable where it flexes the most. or faulty antenna

Oct 23, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

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I have a 148f gtl with no rx on am only,just noise.tx good and rx on side band fine,also tx on am. thanks ,bocephus


Check xtal X1 (7.3450 MHZ). It's in the am osc. I had exactly the same problem. I live in a highly corrosive coastline area

Apr 11, 2009 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Cobra 148 GTL steady tone though speaker


try rerouting your coax cable and make sure it's long enough

Jul 07, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

1 Answer

Cobra 148 gtl stays keyed up on tx on both am and ssb


Your problem is a faulty changeover relay on the circuit board. It is a small black device , and may have the brand name MRATA
etched on it (the switchover contact points are stuck together)
WORTH A TRY GOOD LUCK
flyingfox@prople.net.au

Mar 30, 2008 | Cobra 148 GTL 120-Channels Base CB Radio

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