Cobra 142 GTL swr/mod meter

[Sammitch]

Hello everyone, I have a 142gtl that is almost pristine. I just changed all the electrolytic caps and she talks and sounds great. The only problem I have not been able to track down is the swr/mod meter not working as it should. It will not go all the way over to the cal position when turning the pot so you can check the swr, and the mod . part of it will work in AM, but no movement in SSB.
Do I have a bad meter? Or maybe a bad mod/cal/swr switch? I do not understand why modulation will show in AM but not in sideband. The SRF meter works great, power out matches an external meter perfectly and shows all receive signal strengths.
Anyone have any ideas on what to check or replace? I was hoping the recapping would help, but it did not seem to have any affect on this meter problem. I would love to fix this as it is all that is wrong with the radio, everything else works just fine.

I would love to hear of a fix. I cannot find anything about it in doing searches.

Thanks, Mike

 

[ExitThirteen]

The meter is not supposed to move in SSB mode. Since there is no carrier on SSB, there's no way for the radio to read modulation correctly, and the meter is turned off. The meter is working if it calibrates/reads SWR and reads modulation in AM mode.



~Cheers~

 

[Sammitch]

The meter is not supposed to move in SSB mode. Since there is no carrier on SSB, there's no way for the radio to read modulation correctly, and the meter is turned off. The meter is working if it calibrates/reads SWR and reads modulation in AM mode.



~Cheers~

The modulation part of the meter seems to work in AM, but when you try to adjust the calibration, it will not go over to the cal mark. It just goes over about 3/4 of the way and you run out of turn on the calibration pot. The meter is not stuck, I removed it and checked it by moving the needle with my finger and it is free and easy to move and returns to the starting point every time.
There are 3 resistors on the switch board, any chance the one for the swr could have climbed higher in resistance with age? I am kind of grasping at straws here.

Thank you for the quick reply, Mike

 

[bassman21]

It's possible you have too low of a dead key to calibrate it.

 

[sonoma]

most radios need a 3 to 4 watt dead key to make the meter go over far enough to get a good reading. what watts is you radio putting out? bassman just mentioned that also

 

[Sammitch]

most radios need a 3 to 4 watt dead key to make the meter go over far enough to get a good reading. what watts is you radio putting out? bassman just mentioned that also

After I recapped it, I checked it and it was about 2 watts on both the internal and an external meter. I just figured I would leave it there since it still has the original driver and final in it and not push things too much. That does make sense now that I think about it.
I will turn it up to about 3 1/2 later today and let you all know if that did the trick.

Thanks for the info, Mike

 

[Sammitch]

After I recapped it, I checked it and it was about 2 watts on both the internal and an external meter. I just figured I would leave it there since it still has the original driver and final in it and not push things too much. That does make sense now that I think about it.
I will turn it up to about 3 1/2 later today and let you all know if that did the trick.

Thanks for the info, Mike

Well, I turned up the wattage and yes that seems to be it. Only problem was I had to turn it all the way up to just get the meter to the edge of the cal mark. Then I compared the internal against the external and they no longer match. The internal showed 4 watts, the external showed almost 6 watts. I would like for the meter to work, but I don't want to run the wattage at the max. I backed it down to 4 watts on my external meter.
It will calibrate the external meter, but not the internal. I have no swr problems, so it really is not all that big of a deal. I just thought it would be nice if the old girl would work like she was intended.
If anybody has any other ideas to make the meter work I would appreciate hearing them.

Thanks everyone, Mike

 

[M0GVZ]

Have you tried it with a dummy load or are you connected to an antenna? Always check such alignments on a dummy load as an antenna can cause issues that can affect readings.

 

[kaos513]

ah you beat me to it lol

 

[Sammitch]

ah you beat me to it lol

Yes, I use a dummy load. As a matter of fact, I checked it both on an antenna and my dummy load, readings were very close, the antenna was a little different but not much.
I have an Imaxx 2000 and the swr is 1.1. The radio is working great, everyone says it sounds terrific. I am wondering if the meter could be the problem, I am going to check and see if I can find a replacement. I have a 139xlr that I have been trying to get fixed,
it won't tx or rx. I may swap the meters and see if that is it.

Thanks for the help, Mike

 

[222DBFL]

If the meter works on other functions as it's supposed to, then I wouldn't think it would be the the meter, but something in the circuit for the function that is not working correctly. But I could be totally wrong. If the meter will swing all the way over on other functions, then I would start checking all solder joints, and traces. And also check the Gain knob for the calibration on the front of the radio. Maybe it's dirty or not working properly. Just some other things to consider. Also check the switch got the functions you listed. Maybe check the 3 resistors for being good as well.
Hope you get it fixed. Keep us posted as to if the other meter you have works correctly. Again, good luck and be safe!!! Good day.