Hiya Guys! New guy on the forum, I'm a pretty good radio tech, but this one kinda has me stumped since I'm new to this particular radio. I have a Texas Ranger TR-296GK, basically a Cobra 148GTL, with low TX power in all modes. What happened is..I was monitoring 38 LSB for a friend, and dozed off, and accidentally hit the lock button on my Turner desk mic and left it keyed down for an extended period of time. When I woke up, the radio was scorching hot, so I turned it off, figuring that I had toasted my finals, and went back to sleep. The next morning I tested it, and it works in all modes, just with greatly reduced power. I went from 20-25 watts LSB down to about 8, and a 10 watt AM carrier down to about 2. The audio on transmit still sounds good, and all modes still work, USB,LSB, AM. It doesnt drift on frequency, and receives great as ever. VR10 and VR11 have no effect on power output at all anymore. Any ideas? Thanks guys!
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Cobra 148GTL low TX power in all modes
- Thread starter 2CN319
- Start date
Oops..
I had a feeling a might have posted in the wrong section.. :redface: Would any of the mods be kind to a newb and put this post where it belongs? I'm not much for sending radios in, I've heard enough horror stories to make me just think about buying another radio if something goes seriously wrong that I cant fix, and I've brought some pretty beat up radios back from the graveyard that have had the touch of "the golden screwdriver". Thanks again guys!
I had a feeling a might have posted in the wrong section.. :redface: Would any of the mods be kind to a newb and put this post where it belongs? I'm not much for sending radios in, I've heard enough horror stories to make me just think about buying another radio if something goes seriously wrong that I cant fix, and I've brought some pretty beat up radios back from the graveyard that have had the touch of "the golden screwdriver". Thanks again guys!
Hello, welcome to the forum.
That radio has a single 2sc1969 output transistor in it, I am not sure what power meter you are using but to ask that final to do a ten watt dead key on AM mode is an awful lot.
That is what one usually see`s from a dual final radio.
If you were on SSB and there was no audio going to the radio, there should have been (almost ) almost no power output.......anyway.
I am sure you looked to see if anything looks physically burnt , Check TR-36 the 2sc1969 Final, the power output you see may be what is leaking past a blown final I would also check TR-38 the driver 2sc2166 and TR-39 the pre-driver 2sc2538, but test the final first it may be toast.
Good Luck.
73
Jeff
That radio has a single 2sc1969 output transistor in it, I am not sure what power meter you are using but to ask that final to do a ten watt dead key on AM mode is an awful lot.
That is what one usually see`s from a dual final radio.
If you were on SSB and there was no audio going to the radio, there should have been (almost ) almost no power output.......anyway.
I am sure you looked to see if anything looks physically burnt , Check TR-36 the 2sc1969 Final, the power output you see may be what is leaking past a blown final I would also check TR-38 the driver 2sc2166 and TR-39 the pre-driver 2sc2538, but test the final first it may be toast.
Good Luck.
73
Jeff
I'm using a Radio Shack SWR/Power meter for my tests. I've looked over the circuit for a long time, and I'm not seeing anything that has visually toasted. The radio is fully functional in all modes, just with reduced power which has me scratching my head. Both VR10 and VR11 have no effect on power output whatsoever, I cant get it to push more than 2-8 watts at best. I've been using it on the air, and get good reports on the audio quality. I have noticed that the mod meter wont go over 8 on sideband or AM, even with the power mic and the mic gain cranked to the point of squeal. Thanks for the replies so far guys!
Hmm, I'd almost suspect that the AM pass regulator transistor could have gone south also. Definitely check the final, but also check the regulator transistor too. It's located near the audio IC by where your 12V comes in. This could either be a 2SB827, or possibly a 2SA1869 or 2SC4369. Wouldn't hurt to check/replace this also. But I'm guessing most likely it's the final. Let us know how you get on.
~Cheers~
~Cheers~