No Mic Audio Cobra 148 GTL

[HavaV10]

Also noticed that TR25 and TR26 are missing.

 

[HavaV10]

IC4 voltages

RX Pin 1 8.3 Pin 2 14.2 Pin 3 8.3 Pin 4 0 Pin 5 14.4 Pin 6 8.3 Pin 7 not there Pin 8 0
TX Pin 1 8.3 Pin 2 13.5 Pin 3 8.3 Pin 4 0 Pin 5 0 Pin 6 0 Pin 7 not there Pin 8 8.3

Does this look normal or should I replace IC4

 

[nomadradio]

Making me wonder if someone clipped the wrong part trying to disable limiting. Unsolder the base lead of TR24 and see if this gets you mike audio. Or, poke a meter probe at the base and see if you have 2/3 of a Volt or so. Should be zero with no sound to the mike. If disabling TR24 restores audio, a rogue current source is reaching TR24 base causing it to clamp audio to ground.

TR25 needs to be there so you'll have sideband limiting. The sideband ALC TR34 feeds TR25 for sideband, where TR26 does the same thing for AM only.

Maybe. Running out of common causes.

73

 

[HavaV10]

Making me wonder if someone clipped the wrong part trying to disable limiting. Unsolder the base lead of TR24 and see if this gets you mike audio. Or, poke a meter probe at the base and see if you have 2/3 of a Volt or so. Should be zero with no sound to the mike. If disabling TR24 restores audio, a rogue current source is reaching TR24 base causing it to clamp audio to ground.

TR25 needs to be there so you'll have sideband limiting. The sideband ALC TR34 feeds TR25 for sideband, where TR26 does the same thing for AM only.

Maybe. Running out of common causes.

73

Thanks nomad, I recapped the whole radio today and re installed TR25 and 26. I will remove TR24 and see what that does. I also have IC4 on order. Will change that out once I get it.

 

[HavaV10]

UPDATE...... The Cobra 148 GTL is fixed and the problem was the 1K Dynamike Potentiometer. Put a new one in and bam! We got good loud mic audio. Thanks to everyone that responded with your suggestions.

 

[nomadradio]

Gotta love it when a plan comes together. Didn't think to suggest that one. Not the most common fault.

Congratulations!

73

 

[HavaV10]

Gotta love it when a plan comes together. Didn't think to suggest that one. Not the most common fault.

Congratulations!

73

yeah a friend helped me track down the problem on the phone. shorted 2 terminals together on the dynamike pot and boom the audio was back. I had a 1K in stock over here so got it replaced the 148 is working like new again. I have never had a Potentiometer go bad on me ever. Now I know. Thanks for your suggestions Nomadradio

 

[HavaV10]

Picked up this Taiwan made Cobra 148 GTL the other day. Very clean inside and hasn't been chopped up. No extra channels either. It has a issue, no audio going through when the mic is keyed up. Also the Green/Red led does not turn red when the mic is keyed up. Also no audio coming out of the PA jack. Everything else works perfect. There is good 4 watts output on AM. Maybe someone could tell me a component to check. Maybe TR23 and TR24? Both should be C945 but in loc TR23 there is a C458 in there. In the photo I'm keying up the mic on SSB no red led TX light. Thanks for any help.

UPDATE: Problem resolved! Was a bad 1K Dynamike Potentiometer. Replaced and works like new. Bi-color LED red/green red is burnt out and will be replacing the RX/TX LED soon.