[Elecraft] KX1 RX deaf after KB3080 installation

[Bruce Grubbs]

------------------------
> 
> If you can see the 1 ohm or so difference that represents the resistance of
> L6 when measuring from each end of it to ground, you can tell which side the
> short is on without lifting one lead: it'll be on the end with the lower
> resistance to ground. That will tell you whether to look in the direction of
> T2 or toward Q7. 
> 
> The other possibility to a shorted Q7 is that Q7 is somehow locked "on".
> There should be no bias to ground on the base of it to leave it off. If
> there's about 0.6 VDC at the base then it's being held on by a current
> through R2 that should not be there in receive mode. If that seems to be
> case, grounding R2 at the end connected to the base of Q7 will turn it "off"
> and make the short go away. 
> 
> Ron AC7AC 

Looks like it's Q7. I pulled T2-2 and still had the short. So I pulled Q7. The 
short went away at L6 and the RX works. Q7 is shorted- only 3 ohms collector 
to emitter. I don't think it's not a random failure. The original problem 
with the KXB3080 was a hot Q6 but very low output power. That problem was 
caused by a solder bridge between B and A on the KXB3080 so I'll bet too much 
TX RF got into Q7 and fried it. If I'd caught the problem during RX testing I 
would have avoided this.

At least I can play with the receiver while I wait for a new Q7. The 
sensitivity does seem improved, at least on 20 m, by the KXB3080.

Thanks Ron, Don, and Alexandra, for all the help!

73, 
Bruce
N7CEE