Re: [K2]K2 filters continue to "drift" out of alignment

Posted by K1FFX on Nov 04, 2015; 5:30pm
URL: http://elecraft.85.s1.nabble.com/K2-K2-filters-continue-to-drift-out-of-alignment-tp7609910p7609932.html

Don Wilhelm-4 wrote

The bottom line is that the BFO frequency is 'drifting'.
The most probable cause is a defective solder connection in the BFO area.
Carefully lift L33 and reflow the soldering of the BFO crystals. Reflow
the soldering of C173 and C174, RP6. D37, D38, C169 and Q24.
Make certain when you replace L33 that the leads of the resistor are
well soldered and the leads of L33 are soldered to the resistor leads.

Thanks for the specific and detailed hints, Don (and thanks also to Matt and Bob for helpful e-mails).  I decided to defer handling L33 and the two BFO crystals.  I went ahead and reflowed the soldering for the other components.  This has fixed the immediate problem: the center frequencies moved "up" and was I able to easily align all the filters.  Hopefully, this will be a permanent fix and there will be no further significant BFO drift.  If I continue to see drift, then I'll go ahead deal with L33 (whose solder joints all looked fine to me yesterday) and reflow the BFO crystals' soldered leads.

Thanks again!

- Bruce K1FFX