[Elecraft] Update -- KB1QBZ K2: Various Receive Problems

[Jon Perelstein]

I redid all the Alignment and Test, Part II steps starting on pg. 63, plus checked the VCO frequency at the low end of each band against the chart at the lower left corner of the Schematic Key sheet in Appendix B of the manual.  In doing all that, I re-ran the VFO Linearization (which my notes show that I successfully ran on 10/28/08).
 
Everything tested out correctly, except that on the VCO frequency test my 60m and 30m numbers were a bit beyond the +/- 40KHz that Don suggested.  However, I ran this test before I re-did the PLL linearization, so I need to re-run it.
 
After finishing the tests, I'm now getting a change in pitch as I tune across a signal.  In addition, I can now hear things even with filter 4 in use.  I guess that I somehow managed to get the PLL un-linearized while I was finishing the build and doing the Part III Alignment and Test.  Not quite sure how I did it, but never put it beyond my abilities to do something like that ...
 
Given that AGC was mentioned by both of you, I also re-ran the "Setting The AGC Threshold" on page 48.  I could not get a reading of 3.8 volts on pin 5 of U2.  The best I could get was just over 3.5 volts.  I see from my notes that I had to crank R1 all the way to get 3.8 volts when I did this test a couple of weeks ago.  Looks like there's an issue there.
 
I'm still getting a situation in which a stronger CW signals will completely wipe a weaker one I tune across the band if they're close to each other in frequency.  Thus, I'm still getting that effect of a signal either being there or not being there, with a very narrow bandwidth on signals that are close to each other.
 
Unfortunately, the people who pay me a salary actually want me to do some useful work for them, so I haven't been able to explore these problems any further.  I was going to check components in the AGC area plus check my solder joints, make sure I haven't reversed anything, check the voltages per Appendix E, etc., but that might have to wait a day or two.
 
One thing -- when I was building the set, I did notice that the resistance of pins 7/8 and pins 9/10 of RP5 was not 470 ohms AFTER I mounted RP5 on the RF board.  I just don't see from the schematic why I wouldn't be getting 470 ohms, but I'm relatively new at reading schematics.  Those two pin sets are used in the AF Amp, so it's not clear to me if that would have anything to do with my problem.
 
Thanks for your help so far.  If you have any suggestions that would help me short-cut some of the testing, I would appreciate it. 
 
Jon
KB1QBZ


      
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