Guide :Radio Communications : 148 GTL 120-Channels Base CB Radio

Not working Hi, cobra148gtl-40 channel has no modulation thought the mic and there is no audio or sound, the mic works thought the pa. the needle moves when you modulate but not when you are receiving. thanks

Posted by darren zimmer on Jun 28, 2007

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Suggested Questions And Answer :

Not working Hi, cobra148gtl-40 channel has no modulation thought the mic and there is no audio or sound, the mic works thought the pa. the needle moves when you modulate but not when you are receiving. thanks

Crafties is probably right the part you will be looking for is IC6 it's a AF power amp part number TA7222P located with the radio front faceing you and component side up it's on the right side of board twards the back and fastened to the side of the chassie the chassie is used as the heat sink it is a 10 pin in line part.Be sure to use heat sink compound on the new one when fastening it to the chassie. Good Luck
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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?
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Corba 2000GTL # 53003909 Low are no transmit.. Bought off E-Bay...Had factor hand mic..Has extra channel witch are selected at the sp1 and sp2 selector switch.Both meter were stuck,It would transmit at first light would dim during modulation,and would cal in swr mod.Repace both meters clean up board.Seem to quit transmiting,so replace mic with turner plus 3. Receive well and shows modulation on am,but doesnt seem to trasmit any more.Radio will power up with power switch in the off postion if Turner three mic is in Electonic position at selector switch.

The problem with these radios (I have owned 4 of them and also repaired them) is that if they were "tweaked" too high several bad things can happen.If you have both AM and SSB transmit but it is very low output--suspect either the Driver or Final transistor are bad. You will need to unsolder all three leads (ECB) on each transistor and test them with a ohm meter.If either is bad----replace both--also note which transistors are in the radio--some people will replace them with "higher" output transistors to get more output. If the radio had modifications for a carrier control---it would only affect output on AM.The weak point in this radio if it has been tweaked is the voltage regulator IC located on the right wall of the set next to the audio output IC chip.Checking voltages will not really tell you very much---Confirm first the actual condition of Driver and Final transistors. Some good advice would be if replacing them restores transmit instantly lower both AM and SSB output either with the controls or by alignment of the driver and final stages of the radio.The fact that the radio was dimming the meter lights before is a dead giveaway that the radio was pulling maximum voltage from the regulator IC in the radio's power supply.Something else you may want to try that may or may not confirm this is switch the switch on the back of the radio and connect it to the DC power socket----IF RADIO WORKS THAT WAY-internal power supply is damaged and not the Driver/Final stage.Let me know what you find.SD TECH
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148NW ST No TX AM or SSB

Finals need to be replaced, as they are fried,, hence no output,,and if you are lucky you haven't fried the pre-amp as the pre amp is REAL stop keying it up
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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.

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.
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NO MODULATION I just purchased a Cobra GTL 142 off of ebay. The radio receives great but does not transmit. in fact when you key the mic, the needle on the transmit meter goes toi the left. My mife is out in the back yard bon the mobil in the truck, and she can't hear anything. WHAT GIVES ?

Have the mic checked
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Microphone wiring Tried to wire Astatic d104 microphone to peaked galaxy 88 cb radio. Used 1 shield 2 white 3 red 4 black w/ talk back off. Radio transmits and receives but squeals. Turned down modulation knobs but very little to no audio modulation. Switch in d104 in E position. What's the problem? Stock mic. Works with stock Mic. fine.

The rf power going out is geting inducted on the wires of the mic.try using some ferrites close to the coax on the pl259 connector and on the mic wire itself.
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Magnum 257 No Audio Being Transmitted

Hello.I have a similar situation on a Magnum 257 HP operating on SSB (AM and FM works fine). If i Transmit it works fine, but when i release the Mic button (after TX), in the bottom side were the RX level should be, it appear somth like a signal level 3 to 5 (constant and continous), but i can't get any reception at all. Only if i turn the TX power level to MAXand i transmit, then it goes back to reception, but not every time. Somtime after TX i need to push the mic button 2-3 times to make it recive somthing, but this wors only if the power level is over 60-70% an i repeat, only on SSB.Can i get some help with this issue?
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Sounds to me like the final driver is blown, try replaceing it with a new one.
Read More At : 148 GTL 120-Channels Base CB Radio...

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