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Cobra 29 LX No TX

Unit 75

"TRAINMAN"
Jul 29, 2014
526
1,022
153
Central Alabama
I have a Cobra 29 LX made in China. The radio worked fine. I keyed it up and unkeyed it about 4 times in a row into a dummy load and it just stopped transmitting after that. Receive works fine. The PA works fine. The radio does go into tx mode on the display but has no RF output or modulation. I have replaced both driver and final and still no output. Is there some inherent problem that some of you 29 Gurus know about? Thanks.


Update: Made a sniffer antenna and hooked it to a test radio on the same channel. I held it near the driver and final while I keyed. The test radio's meter showed some signal. I also retuned L21, L20 and L17 for max. I am still not getting any real wattage out that my wattmeter can measure, I cannot even see a needle deflection on the 10w scale.
 
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I checked IC3 (TA7310P) and have my 10.245MHz on pin4, my 16+ MHz on pin1 and my 27+ MHz out on pin9. All other voltages on this mixer are good, so I can rule it out. TR14, TR15, TR16 are all good. Voltages in tx mode are what they are supposed to be. The audio transformer and diode are good as well. Looks like my signal is being lost between the mixer and the final somewhere. still looking.....
 

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