Well, I messed around with it a bit more and I gave L33 and very light nudge with the plastic tuning tool while looking at CAL FCTR. This caused the BFO frequency to suddenly jump down from 4913.30 to 4912.42.
Strange thing is, only a few minutes after nudging L33, the BFO frequency had already drifted 100Hz up and still drifting. I give it another nudge and it drops down again but then eventually resumes drifting upward. I also measured the VBFO voltage, as you suggested, before and after, and there is no change even as it resumes drifting. I had already removed and re-soldered L33 and the 1/8W resistor holding in place about a week ago. I have also put a couple pieces of heatshrink tubing on the leads of the resistor to ensure they aren't shorting on L33's turns. This did not make any difference. I also confirmed the solder connection is good by measuring the resistance across the pads of L33: 0.3 ohms. Starting to look like L33 might be defective? Still puzzling why giving it a small nudge would cause it to behave temporarily again. I'm not even touching the windings just gently pressing down a bit on the part of the core that isn't covered in turns. I also used the tuning tool to apply a bit of pressure to the other components associated with the BFO, as well as their soldered pins, and couldn't cause any change by doing that, nor did reflowing any of the solder joints do anything. I wish I had an LCR meter, I'd remove L33 and hook it up to the meter overnight looking for any drift in its inductance. Unfortunately that is an instrument I do not have. Thanks for the help. On Sun, Apr 13, 2014 at 11:43 AM, Don Wilhelm <w3...@embarqmail.com> wrote: > Some component (or components) in your BFO (or the generation of the VBFO > signal) is changing characteristics. > It could be the crystals (X3 and X4) or the capacitors (C173 and C174) or > the varactors (D37 and D38), or L33. > It also could be soldering on the R-Pak RP6 or any of the above components. > Since my first guess is that there is a solder connection that is slowly > gaining oxidation, I would re-solder all the components in question before > doing anything else - use a hot (750 degF) iron and add just a tad of flux > from a bit of new solder. > > There is also the possibility that the VBFO signal coming from the Control > Board is varying. This is a DC level that tells the varactors how much to > change capacity. > To check that, leave one filter set the same at all times. With that filter > selected, measure and record the VBFO value to as many significant digits as > your DMM will show. Control Board U10 pin 14 is an easy place to measure > it. Then when the BFO shifts frequency, measure it again (do not change > that filter setting). If the voltage changes, then the problem may be with > U10 on the control board. Re-solder U10 and RP2 and RP3 to see if that > stops the change. > > On 4/13/2014 1:24 PM, TheMG . wrote: >> >> Well, a few weeks ago I finished assembling and testing my K2 S/N 7520 and >> the KPA100, KSB2, K60XV, and K160RX options. All went without any problems >> at and have had several successful QSO with it. >> >> However, since then I've been noticing quite severe BFO drift. I have to >> re-align the filters using CAL FIL almost daily. The low range of the BFO >> keeps drifting upward, about 50-100Hz every day, and it hasn't stopped yet >> even after two weeks! >> >> Initially (first built and tested), the BFO low range (as measured with >> CAL >> FCTR) was at 4912.6kHz. Today it's at 4913.35kHz. >> >> What I've ruled out so far: >> >> -Temperature. Room temperature is quite stable around 20-22C. Even after >> long periods of transmitting with the KPA100 and the entire K2 chassis >> getting quite a lot warmer than room temperature, BFO temp-related drift >> was only about 30Hz and in the opposite direction of the daily BFO drift >> of >> 50-100Hz. >> >> -At first I though maybe I hadn't properly secured L33 and that maybe >> mechanical vibrations and stress from moving the K2 around was causing the >> inductor to move around, but for the last week I had it sitting on a desk >> without moving it at all and the BFO is still drifting. >> >> Also, from my observations, the BFO range is actually constricting, rather >> than simply shifting upward. The high range of the BFO has gone from >> 4917.47 to 4917.15. >> >> Gently tapping or pressing on the RF board doesn't change anything. >> >> Anyone experienced anything like this or having any idea what the problem >> might be? >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
