Help... Cobra 148 GTL no voice TX in AM FM SSB- RX OK

[papafina]

Cobra 148 GTL - it does not emit the signal of voice in way TX, only the carrier of Harnesses, I changed already the MB3756 and nothing, they can give a tip.

73/51

Edison Portugal
Carlos

[Rick]

Check to see if the PA is working. If not check, you have a good mic also check TR21, 22, 23, 24, 25, 26, and 27. I have had TR27 go short, which causes the radio to stay in the PA mode. Hope this helps.

Rick.

[papafina]

OK Rick the PA is?not OK, the microphone this good one, I go to test the TR21, 22, 23, 24, 25, 26, ai change TR 27 and nothing.
if to change the button for PA, I hear the RX in position PA a little low de sound.

73/51
Carlos

[ramblingman]

hello,,for no tx audio,with good dead key.check c-18 for short

[papafina]

hello ramblingman, ai change the c-18 and nothing... Gracias
I am wait for the TR21, 22, 23, 24, 25, 26, 27 transitores to change later I say some thing...
73/51
Carlos

[papafina]

Ai change the TR21, 22, 23, 24, 25, 26, 27 transitores, and nothing, can yu hellp me.
I tested the D61,60,59, C99 and are good,
I have the sound of the RX in the PA,
if I injectar sound collector of TR 21, I have TX OK
but if to injectar the same sound in the L404 I do not have TX
can help me...
the PA does not function.
I hear a small snore, when I load PTT to TX, as it was an feeding snore type.
much I am thankful for your attention...

73/51

Carlos

[Rick]

Try injecting audio at C108 and collector of TR23, TR24. Let us know how you get on.

Rick.

[papafina]

thanked Rick,
but it continues equal, I have only carrying of AM and SSB I followed your suggestion but it did not give nothing

I injecting audio at C108 and collector of TR23, TR24, and did not make nothing.
I repaired that the tension of transistors TR21, 22, 23, 24, 25, 26, 27, they are different of the mentioned one of the project of the manufacturer,
They are very low, I do not only understand because it makes a racket of deep in way of TX in AM and SSB.

if to put the tip of tests of the multimeter in the sender of the TR21 and squeeze the PTT the Carrier of AM leaves without racket.
perhaps this says some thing to you.

very I am been thankful by your aid...

73/51
Carlos

[Rick]

It sounds like you have the radio in the PA mode or AMC/ALC transistor TR24 is turn-on, try removing C110 and see if it is now working, if not try removing TR24 and see if it is now working.

TR24 is used to shunt the mic audio to ground, this is part of the ALC and AMC, and if this transistor is fully turn-on then you will have no TX audio.

If the above does not help can you let me have the voltages of transistors TR21, TR22, TR23, TR24, TR25, TR26, and TR22 with the radio in the TX mode?

You may find this diagram easy to work with.
http://www.cbtricks.com/radios/cobra/14 ... redraw.pdf


Rick.

[frogman296]

It sounds like you have the radio in the PA mode or AMC/ALC transistor TR24 is turn-on, try removing C110 and see if it is now working, if not try removing TR24 and see if it is now working.

TR24 is used to shunt the mic audio to ground, this is part of the ALC and AMC, and if this transistor is fully turn-on then you will have no TX audio.

If the above does not help can you let me have the voltages of transistors TR21, TR22, TR23, TR24, TR25, TR26, and TR22 with the radio in the TX mode?

You may find this diagram easy to work with.
http://www.cbtricks.com/radios/cobra/14 ... redraw.pdf


Rick.

i have the same issue rick... with the same radio...

replaced mb3756, ta7222ap... various caps that have been know to cause the same symptoms...

have tried removing c110, and tr24... still nothing... get a good strong carrier on AM... no modulation/audio in any mode.....tx light comes on when txing

it all started when i removed a home brew echo board...i didnt change anything as far as wires go, i even put two radios side by side and made sure everything was up to snuff in the line of wires.

should i replace some transistors?

[The Defpom]

Do you have audio in PA mode ?

If not trace all the way from the audio pin on the mic socket through to the main PCB, and confirm that there are no shorts or missing connections, a solder blob could kill the audio entirely, even with connections being correct.

[frogman296]

Do you have audio in PA mode ?

If not trace all the way from the audio pin on the mic socket through to the main PCB, and confirm that there are no shorts or missing connections, a solder blob could kill the audio entirely, even with connections being correct.

no audio in pa mode... i get some "fuzz" when i key the mic in PA mode..

will trace it soon