David,
To test, turn on the preamp and tap Q21 with a screwdriver tip - you can
tell when the sharp 'clicking' with each tap is taken out by the KNB2.
There is not a lot of circuitry on the KNB2, so I suggest that you check
all the components for correct values, and in the right positions. Make
certain the diodes are oriented in the correct direction.
Look at the schematic and identify the voltages that will be present for
the 2 thresholds (U3 pin 6) and the two pulse widths (U3 pin 7). If you
have a logic probe or better yet a 'scope, you should be able to see if
the one-shot is producing gate pulses (collector of Q4).
Remember the most common cause of problems is the soldering followed by
poorly tinned toroid leads and misplaced components - check these
carefully as your first efforts, try to look at it critically as though
someone else had built it.
73,
Don W3FPR
David N. wrote:
Ok I have gone over my KNB2 Board twice now to see why
it will not blank any noise. I had a friend of mine
come over here with his and we used my noise source.
(1948 Ferguson Tractor) Noisy ignition. He set his for
nb1 and badda bing badda boom all gone mine still
there. NB2 Still there. I asked hime if he did
anything to his and He said nope just the way it came.
I did research through the archives and found a note
about scratching the surface of Q22 But that is not
possible on mine it is under the NB2 Board. So What
can I do to troubleshoot mine.
Thanks
David KR4OW
K2 4320
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