[Elecraft] KNB2 diagnosis

[johnfm1 at optonline.net]

Chris,
I installed a KNB2 in my K2 a few months ago. I didn't think it worked until I tried the scratching of Q21 as recommended.
 
With the top off and background noise coming from the speaker, I toggled from NB1 to NB2 to OFF while I scratched the case of Q21. It worked. I saw a definite difference. 
 
With the NB on I then toggled between both threshold levels and heard the difference also.
 
Give this technique another try. Use a small screwdriver to scratch with. 
 
Good luck.
 
John N2YC
 
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