Ken, The "fuzzy" waveform on the 'scope is normal - but how much so is difficult for me to say whether yours is normal or abnormal.
Check the value of C169 - it should be 390 pF (marked 391). OK, the BFO is oscillating, so look at Q24 carefully - is it oriented correctly? If so, enter CAL FCTR and tap the BAND+ button while measuring the voltage on the drain (see the schemastic key page if you are not familiar with the pinout). The voltage should go high(almost 8 volts), and then tap BAND- and the voltage should go nearly to zero. Other things to check - look for a solder bridge between pins 1 and 2 of U10;, check the SMT1B for correct orientation; re-check the orientation of D36, and check the soldering of R98, C168, D36, R99 and SMT1B. If all the above is correct, try replacing Q24. If you have a J309 around, try that (if you have the KDSP2 kit, there are J309s in there). 73, Don W3FPR Ken Mohler wrote: > Don - > > You have me on the right track. I have a valid frequency reading at pin 6 > of U11 and I can follow it back through L33 and C169 to the gate of Q24. The > waveform gets fuzzier and has lower amplitude past L33 (I do have a scope) > but is still countable at C169. Past Q24 I don't have anything > recognizable. I have reflowed the solder on everything around there. D36 > appears to be installed correctly. I don't have an extra J310 to swap out > Q24, but will get one if you think that's the next step. BTW, I measured > the voltages at U11 and all are what you told me to expect except pin 8 is > around 6 volts. Still, the BFO seems to be working, just not getting > anything as far as TP2. Thanks for the help and please keep it coming. > > 73, > Ken > K0WKM > > -----Original Message----- > From: Don Wilhelm [mailto:w3...@embarqmail.com] > Sent: Friday, July 16, 2010 6:49 PM > To: Ken Mohler > Cc: elecraft@mailman.qth.net > Subject: Re: [Elecraft] K2 BFO problem > > Ken, > > Did you obtain a good frequency reading when you did the PLL Reference > Oscillator test back on page 36? If so, check the probe again by > putting the probe into either TP3 or TP1. If you see a valid frequency > displayed, your probe is OK. > > The most common problem builders have are soldering problems. Re-flow > the soldering in the BFO and U11 area with a hot soldering iron (750 > deg/F). Also check carefully for solder bridges. Unfortunately, one > lead of both X3 and X4 are under the pad for L33, so ignore those for > the time being (if nothing else works, Lift one end of the resistor > securing L33 and re-flow the soldering at those leads). > Do you have near 8 volts at U11 pin 8? Is U11 pin 1 and 2 close to 1.4 > volts? Do you have about 6 volts at U11 pin 6? > > Touch the counter probe to U11 pin 6 (careful not to short to an > adjacent pin). Do you have a valid frequency reading? If you do, then > the BFO is working, and the problem is with Q24 and its associated > components. Be certain you have mounted D36 (the SMT1B) part correctly, > and the soldering of Q24, RP6, R98, and R99 is good. > > If still no progress, either assemble the parts provided in your K2 kit > for the RF Probe (schematic in Appendix E) or let us know that you have > an oscilloscope available. > > 73, > Don W3FPR > > Ken Mohler wrote: > >> Hi Gang - >> >> >> >> I'm building my 2nd K2 and am at the point of Alignment and Test, Part II. >> All of the tests and alignment steps through the VCO alignment have been >> completed successfully. Everything has been right in the center of the >> expected parameters. Then I got to the BFO test. I'm getting a reading >> > of > >> 0000.00. Here's what I know so far: D37 and D38 are the correct types >> > and > >> oriented properly. I have measured the resistance across the resistor >> holding L33 down (or up?) and get a reading of 1.5 ohms, indicating to me >> that L33 is intact and effectively soldered to the resistor leads. I have >> checked the positioning of Q24 and it looks correct. The right crystals >> > are > >> installed at X3 and X4 and grounding the cases went smoothly, so I don't >> think I overheated them. I have reflowed the solder on the parts around >> > the > >> BFO area. A symptom that may or may not mean anything: the S-Meter is >> showing S5. It was properly adjusted back in Alignment and Testing Part >> > I. > >> What should I do next? >> >> >> > > ______________________________________________________________ > 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 > > ______________________________________________________________ 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
