[Elecraft] KNB2 diagnosis

[Christopher A. Kantarjiev]

I've never been convinced that my KNB2 worked as planned. I have the K2 open 
today to install the K160RX, and decided to work on the KNB2.

I found the archive messages about "scratching" Q21. I can only get any noise 
out of this with the pre-amp on - don't know if that's as expected or not. No 
setting of the NB changes the audio through the headphones.

I can tap Q21 and get a pulse on my scope, or rub the case back and forth to get 
something a little more continuous (but still hard to capture on the scope - 
despite being quite evident in the headphones).

Some of the time, my pulses just die at the output of R8, which goes to ground 
via L1. I'm not sure exactly what I do differently when the pulse gets past - 
perhaps just how hard I'm tapping?

If I have the NB turned off, the signal stops at pin 4 of U1 - I see pulses 
there, but not at pin 1.

If I have the NB turned on, pin 4 is biased and pin 1 is biased even higher - 
but I don't see the pulses at either pin.

Help? Feeling stuck here.

73 de chris K6DBG