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Cobra 142GTL No Transmit or Receive

I removed the Anode wire at the base of TR40 from the main board and tested.

Positive lead from meter to anode side of diode reads 1.138
Negative lead from meter to anode side of diode reads .0L

Seems Ok. Not sure what the voltage drop of the mv-13 diode should be.
2 1n4148s in series is 1.160..
 
That sounds right. I wonder if it is possible that when we tested TR40 if the b-e junction was shorted and we saw a lower voltage because the final base held it down. The only thing I can think to do at this point is to remove TR40 and test it out of circuit.

I want to say it is ok but I am running out of ideas here unless someone swapped the VR with a different value. My washington has a 1k there. 5k should be even better if you are getting too much current..
 
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Im guessing now, because when you had tested the base and emitter voltage, it looked good. If the be junction was shorted, the base would have been nearly the same as the emitter.
 
Is your replacement 1969 newer? Maybe they had a slightly different turn on curve than the originals that don't take as much base current. If the VR and everything else tests good, I would triple the resistance of R149 and try setting the bias again.

If someone sees something I'm missing, please chime in!!!
 
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Hold off on reinstalling it for a bit. What value pot is VR9? Is it 5k like the schematic shows, or is it 1k?
 
Actually, go ahead and put it back in. If everything else tests good, you know the VR is good, and you know your transistor is not a counterfeit, put a larger value pot in there (or change R149) to a higher value to lower the current.

If all else is testing good, it must be a gain thing. There is a reason they went from 5k to a 1k (as in my washington). Maybe a part changed during production necessitating the pot change. Maybe someone swapped parts from an older/newer radio that are not quite the same.

The only thing I can figure to do next is to pull my parts and get hFE values to compare to your T40 and T41. I can when I get home.
 
Got pulled away to something else. Just getting back to this.
Looks like the VR9 is reading roughly 1K ohm to about 6K ohm. If I'm looking at this right the bias current is lower when VR9 is turned all the way to the left which is where the VR is reading 1K. Which doesn't make sense to me.

When I get in tomorrow I will increase the value of R149 from 100 ohm to 330 ohm and see if it allows me to adjust VR9 to get 45mA on the final bias.
 
IIRC, with the front of the radio facing you, the leg closest to R149 on the right side and the wiper should increase in resistance as it is turned left (counterclockwise). That should decrease the bias current. I don't think the lower right leg is attached to anything, but I'd have to check when I get home to say for sure. 5k sure should be enough. I was thinking that maybe yours had a 1k like mine.
 
Ok so VR9 is working right. When turned counter clockwise it reads 6.8k ohms when turned clockwise it reads 1.2k ohms.

So I put a 330 ohm resistor at r149 and when checking the bias on the final I read 70mA with VR9 fully counter clockwise put the 100 ohm resistor back at R149 and checked the bias and read 70mA. The bias is actually 17mA higher than it was when I first checked/adjusted it. I don't get it....
 
This is a long shot, but what flux are you using?

Are you cleaning it off? Is it no-clean?
 

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