Congratulations Mikael. That sounds like a tough one to track down. I have seen the symptoms before. While it is possible the rubber was not fully cured, my bet is chemical contamination. The symptoms are classic for acetone contamination. There is a mistaken belief acetone is a great flux remover. It’s not! While it does remove flux, it can cause latent defects that take years to show up. Let me make it clear I am not accusing you of using acetone. I am letting, others who profess the use of acetone for cleaning, know what they can look forward to. By the way, there are other compounds, such as nail polish remover, that contain acetone. Stick to alcohol and you’ll be alright. 73, Fred, AE6QL
-----Original Message----- >From: "TheMG ." <th...@mg3000.net> >Sent: Apr 14, 2014 11:15 PM >To: d...@w3fpr.com >Cc: elecraft@mailman.qth.net >Subject: Re: [Elecraft] K2 BFO drift problem > >Wow, you'll never believe what I just found out! > >There is absolutely nothing wrong at all with L33. It turns out it's >the rubber bumper that is at fault! > >I found this out by pressing down on the stem of the bumper with the >plastic tuning tool, instead of pressing on the inductor. Guess what? >Frequency started to drift!!! > >On a hunch, I decided to get my multimeter and measure on the bottom >of the rubber bumper. It's slightly conductive! Starts at about 3 >megohms and if I hold the multimeter probes in place the resistance >slowly starts to drop down to 1 megohm and below. After a couple >minutes holding the probes in place about 1/4 inch apart on the bottom >of the bumper, the resistance got down to 500k! > >Since the solder pads for X3 BFO crystal are underneath the rubber >bumper, it is effectively like putting a resistor in parallel with the >crystal, which obviously has undesirable effects on the operation of >the BFO oscillator. > >The slowly decreasing resistance as the meter probes are held in >contact with the rubber is consistent with the fact that the BFO >drifts over time. > >I suspected contaminants on the surface of the rubber, but after >cleaning it with iso alcohol, there is no change. Something in the >rubber is causing it to be conductive. > >I wonder if somewhere out there, there are hams with K2s experiencing >BFO drift related to the same cause? If I got a conductive rubber >bumper in my kit, it's highly likely someone else has also. > >Anyways, it's getting a little late right now. I'll communicate my >findings to Elecraft tomorrow (in case they aren't already reading >this). > >73, >Mikael >VE8MT ______________________________________________________________ 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
