Cobra 139xlr

captian_radio · Post by **captian_radio** » Thursday 13th Dec 2007, 15:15

Tonite I turned on my 139 for the 1st time in a while, I went to key it up and no output and some smoke!! I took off the top cover to look around and I see that TR5 seems a bit burnt on the seam at the top and also C12 has the plastic covering melted somewhat,RX is still fine and I can detect some output in another radio.I replaced the final a few months ago.TR5 is a 1730 and was wondering what function this TR does in the radio,I cannot find a block diagram to better trouble shoot this , anyone have any ideas?
Tnx Bob

captian_radio · Post by **captian_radio** » Thursday 13th Dec 2007, 15:48

Update , I did find that R 205 was burnt and looks like it took out the final or the other way around. So there can't be anything wrong with TR5 because I would not have any RX. I will put in another final tomorrow and replace the R205 with a higher wattage and see how that goes.
Bob

sonoma · Post by **sonoma** » Thursday 13th Dec 2007, 20:09

http://cbtricks.com/radios/cobra/139xlr/index.htm

here is the schematic for this radio on cbtricks.hope this helps you

captian_radio · Post by **captian_radio** » Friday 14th Dec 2007, 4:02

Tnx for the link , I did find the link very useful although a block diagram would be nice to have on that site. I will replace the final later today and post my results.I also read some of the tech updates about the fix for this prob of the final going out, upon checking my radio I see that it already has these done , must be a newer version because the updates are factory spec.After I replace the final this time I will check the bias for the final and driver to make sure they are set correctly
Bob

captian_radio · Post by **captian_radio** » Saturday 15th Dec 2007, 11:36

Ok the 139 is up and running again.Replaced the final and the resistor and off to the races again
Bob

Min · Post by **Min** » Saturday 15th Dec 2007, 14:15

Good to hear.