Re: New KX1 low power and 20m oscillation

Posted by Stan Gibbs, KR7C on May 08, 2012; 4:07pm
URL: http://elecraft.85.s1.nabble.com/New-KX1-low-power-and-20m-oscillation-tp7531133p7539677.html

Don Wilhelm-4 wrote

Make certain that Q7 is working.  Capacitor CA is one of the low pass
filter components that must be in the circuit on transmit.  Q7
effectively grounds one side of that capacitor on transmit.

As I said in my original post, Q7 is the place where my DC troubleshooting measurements differed from specs.  The base of Q7, which is supposed to be 0.7V, is -0.895V on 40 and -0.195 on 20.  The voltage on Q7 should definitely be positive in order for it to ground capacitor CA, so something is screwy.
 
Someone suggested that either C45 or C32 were possibly bad, allowing RF on to the base of Q7, which might cause the bogus voltages.  I tried adding additional capacitance in parallel with C45/C32, but that had no effect.