Hi Dave, Don and I have had several exchanges off list, so let me bring you up to speed. In addition to the low VFO frequencies, I had noticed some instability in the frequencies as displayed. Don suggested that I insert a 10-15pf cap between the source of the Q19 FET and ground. I did that late last night and not only did that clear up the frequency instability, but now my VFO frequencies are up about where they are supposed to be (8912 at 4000 and 12013 at 7100). I don't know if adding the cap did all of that or perhaps the process of reflowing the connection on the source pad of the FET straightened things out. So now I'm back to the original problem of the 8.37 V at R30 which has not changed. Don also wanted me to order two J310 FET from Elecraft, but in light of this latest finding I was waiting to see if he still wanted me to do that.
73 de John WB4GLJ On Wed, May 1, 2019 at 9:03 AM Dave Van Wallaghen <d...@w8fgu.com> wrote: > Hi John, > > I just got back in town and I know I'm late into this. I see Don is > stepping you through some things as well. Here are a couple of things I > was > thinking: > > Since you have a VFO output although low in frequency, I think because > the > voltage at pin 7 of U6 is so high it is driving the VFO circuit low in > frequency. 8.37v seems to me to be the 8v rail in that circuit and since > you can't really move that voltage on U6 P7, I might suspect a short > between U6 P7 and P8 or at least a short between U6 P7 and the 8v rail. > > Just something else to look at... > > BTW - Don or I would be the guy to reply from support if you asked > something there. So I just replied to the list so we can keep everything > in > a single thread. > > 73, > Dave, W8FGU > > On April 30, 2019 15:49:42 John Wingard <jwin1...@gmail.com> wrote: > > > Hi Don, > > > > No problem on the delay. OK, after removing 1 turn from T5, the freq. at > > TP1 (at 4000) is now 8535.14, so it did come up from the previous value, > > but clearly not enough. I have 4.19 V on pin 5 of U6 and I have 4.21 V on > > pin 13 of U4. > > > > I wasn't sure of your schedule so I also put in a support request to > > Elecraft but have not received a reply as of yet. Hopefully between your > > help and their help I can get this resolved. > > > > 73 de John, WB4GLJ > > > > On Tue, Apr 30, 2019 at 2:48 PM Don Wilhelm <donw...@embarqmail.com> > wrote: > > > >> John, > >> > >> Where did the TP1 frequency go after you removed a turn? > >> > >> It is possible that the VFO frequency is not getting back to U4 pin 4 -- > >> the signal goes from U3 pin 6 thru C62 and then to U4. > >> > >> Did we verify that U6 pin 5 is near 4 volts? What is the voltage at U4 > >> pin 13? > >> > >> Sorry to go over things, but I just returned from a few days away and my > >> memory is not yet focused. > >> > >> 73,, > >> Don W3FPR > >> > >> On 4/28/2019 6:00 PM, John Wingard wrote: > >> > Don, > >> > > >> > Finally got back to the K2 this afternoon. I have confirmed that T5 is > >> > on the yellow core, with 16 turns through the center on the red and 4 > >> > turns on the green. I mentioned earlier that I got all the toroids > >> > from the Toroid Guy, so I felt confident that it was correctly wound. > >> > I checked all the relay pins on K13, K14, and K15 and did not see any > >> > solder bridges on any of them. Next, I pulled T5 and removed one turn > >> > and re-installed. Unfortunately, nothing has changed. I'm still > >> > getting that same 8.37 V at R30. Incidentally, I'm getting the 8.37 V > >> > on either side of R30. Is that normal? I can also pull T5 and wind a > >> > new one with the parts that came with the kit if you think that might > >> > help, but something tells me that the problem lies elsewhere. I also > >> > thought about pulling C72 and replacing it with another one, but > >> > unfortunately there was only one of that value in the kit and I don't > >> > have anything like it it my parts stash. Any new thoughts? > >> > > >> > de John, WB4GLJ > >> > > >> > > >> > > >> > On Sat, Apr 27, 2019 at 6:00 PM Don Wilhelm <donw...@embarqmail.com > >> > <mailto:donw...@embarqmail.com>> wrote: > >> > > >> > John, > >> > > >> > Both frequencies are too low. > >> > You have either too much capacitance or too much inductance in the > >> > VFO. > >> > Count the number of times the red wire goes through the center of > >> > the T5 > >> > core - it should be 16. > >> > > >> > Check relays K13, K14 and K15 for solder bridges. > >> > > >> > Make sure the core of T5 is yellow. > >> > You might have to try removing a turn from T5 if you can find no > >> > other > >> > cause - there have been a few K2s in the long past where the > >> > permeability if the T5 core was higher than expected, and > removing 1 > >> > turn from T5 corrected things - I have not seen that recently, but > >> > I do > >> > mention it 'just in case'. > >> > > >> > If all else fails, you may have to "wind your way" through the > relay > >> > connections for the VFO Range Select area using the Relay Table on > >> > the > >> > Schematic Key page as your guide for the paths through the relays. > >> > > >> > 73, > >> > Don W3FPR > >> > > >> > On 4/27/2019 5:37 PM, John Wingard wrote: > >> > > Hi Don, > >> > > > >> > > Thanks for the quick response. I did check C72 again. It is a > 271 > >> > > value. I then spread the red turns on T5 as far as I could. I'd > say > >> > > they cover about 90+% of the toroid. I put the L30 slug at > >> > mid-point > >> > > of travel and measured voltage at R30 and it is still right at > 8.37 > >> > > V. While there I checked the frequency at TP1 and it was > 8247.90, > >> > > which is considerably lower than the 8913 that you expected. > >> > > > >> > > Next I went up to 7100 and measured the voltage at R30. Still > >> > right at > >> > > 8.37 V, no change. Frequency at TP1 @ 7100 was 11558.11. > >> > > > >> > > So, it appears that the frequency at 4000 is not within the > >> > expected > >> > > range, and likely not at 7100 as well. Hope this tells you > >> > something > >> > > because I'm stumped. > >> > > I've got some plans for this evening so I may not get back on it > >> > until > >> > > tomorrow afternoon, but if you've got any more things for me to > >> > try I > >> > > will do them then. > >> > > > >> > > John, WB4GLJ > >> > > > >> > > On Sat, Apr 27, 2019 at 1:57 PM Don Wilhelm > >> > <donw...@embarqmail.com <mailto:donw...@embarqmail.com> > >> > > <mailto:donw...@embarqmail.com <mailto:donw...@embarqmail.com > >>> > >> > wrote: > >> > > > >> > > John, > >> > > > >> > > That high voltage is trying to reduce the capacity of the > >> > varactors. > >> > > Which means there is either too much capacity or too much > >> > > inductance in > >> > > the circuit. > >> > > > >> > > Check the value of C72 first - it should be marked "271". > >> > Then set > >> > > the > >> > > L30 slug to about mid-position and spread the red turns of > T5 > >> > > enough so > >> > > the starting and ending turns are adjacent. What is the > >> > voltage when > >> > > tuned to 4000 kHz? Measure the frequency at TP1 - it should > >> > be near > >> > > 8913 kHz. > >> > > > >> > > Then change to 40 meters - 7100 kHz - What is the R30 > >> > voltage and > >> > > what > >> > > is the VFO frequency measured at TP1. > >> > > > >> > > The answer to those questions will help in determining what > >> > to do > >> > > next. > >> > > > >> > > 73, > >> > > Don W3FPR > >> > > > >> > > On 4/27/2019 1:32 PM, John Wingard wrote: > >> > > > Working on my 2nd K2 (S/N 7869) and have run into a > >> > problem with > >> > > the VCO > >> > > > alignment. I'm getting a constant 8.37 V at R30 at 4.000 > >> MHz.. > >> > > I cannot > >> > > > change it with the full range of L30. Correct type > inductor > >> is > >> > > installed at > >> > > > L30. Dropping the VFO down to 3.500 doesn't change it > >> > either. I > >> > > have gone > >> > > > back through the archives and read just about every post > >> > > concerning this > >> > > > problem but nothing I have tried has made any difference. > >> > I have > >> > > double > >> > > > checked all correct parts placements and orientations, > >> > re-flowed all > >> > > > connections in the quadrant of the board around the VCO > >> > section. > >> > > T5 is > >> > > > wound as per the manual (from the Toroid Guy) and > installed > >> > > correctly. I > >> > > > have tried both spreading and compressing the turns on T5 > >> with > >> > > no change > >> > > > either way. > >> > > > > >> > > > Regarding the thermistor board, I have 4.18 V on pin 5 of > >> U6. > >> > > > > >> > > > Test in the previous section were within specs: > >> > > > > >> > > > 4 MHz Oscillator Cal using CAL FCTR was 12099.61 and > >> confirmed > >> > > with an > >> > > > external counter. > >> > > > Range of the PLL reference oscillator: 12099.61 - > 12086.01 = > >> > > 13.59 kHz > >> > > > VCO oscillator test: 8162.60 MHz > >> > > > > >> > > > I'm about out of ideas at this point. What should I start > >> > > checking next? > >> > > > > >> > > > Thanks for any help! > >> > > > > >> > > > 73 de John, WB4GLJ > >> > > > > >> ______________________________________________________________ > >> > > > Elecraft mailing list > >> > > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > >> > > > Help: http://mailman.qth.net/mmfaq.htm > >> > > > Post: mailto:Elecraft@mailman.qth.net > >> > <mailto:Elecraft@mailman.qth.net> > >> > > <mailto:Elecraft@mailman.qth.net > >> > <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 > > > > ______________________________________________________________ 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
