Cobra 139

[Raccoon]

Hi everyone, I have a Cobra 139 base station. The 23 channel version, not the 40 channel XLR version. I plugged it in and everything lights up and looks good . But it has no receive, does anyone here have any idea what might be causing this, because I'd really like to make this radio operational again .

Thanks

 

[doffo]

I had some trouble with a dirty channel selector on my Base 139 23 Channel. This made it where there was no receive/transmit. Maybe change the channel selector a bit a few times back and forth to see if something comes in.

 

[BC Coyote]

Hi everyone, I have a Cobra 139 base station. The 23 channel version, not the 40 channel XLR version. I plugged it in and everything lights up and looks good . But it has no receive, does anyone here have any idea what might be causing this, because I'd really like to make this radio operational again .

That's a really old radio. There are SO many things it could be, but the first one to check is the mic. Most of those older Cobra radios feed the receive audio through the mic switch. If the mic is not connected, or is defective, the radio will remain silent.
If the mic checks out, I would start thinking about getting the radio recapped....

 

[TM86]

What it might be? One or more oscillators failing due to component value drift, bad coupling caps between stages, IF mixer failed, blown speaker voice coil, bad volume pot, oxidation of contacts in the relay or the external speaker jack, oxidation of contacts in the channel selector or mode switch, rodents ate the wires inside, one or more missing voltages from the internal power supply, dead 7.8 MHz filter, dead TR1, or the squelch is just cranked up.

If you have access to the service data, try starting with an alignment and see what fails to align. It's as good a starting point as any when you're not sure what the problem is. And if you don't find anything your radio is properly aligned when you're done. Still broken, perhaps, but properly aligned all the same.

 

[nomadradio]

I would start with cleaning the rotating contacts on the channel selector. They're silver plated and they build up a layer of black tarnish after years of neglect. The gunk insulates the contact surfaces and shuts it down. Radio can't work until all the crystals are running. The relay is an aggravation when it wears out. Put it on an antenna and see if the S-meter kicks around on channel chatter and noise. If so, the receiver is working, but you have an audio problem.

73