---------- Forwarded message --------- From: Keith Hamilton <n8cep.ke...@gmail.com> Date: Mon, Jul 13, 2020 at 9:19 PM Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem To: Dave Van Wallaghen <d...@w8fgu.com>
Dave Yes the frequency changes when turning the VFO knob when measuring with CAL FCTR on TP1. I have checked the markings on C71, C72, C73, and C74 (C75 is not installed yet). They are all correct and I resoldered them to be sure. I am beginning to think I might have a bad relay K13, K14 or K15. My good bands are 80,40 and 15 meters. My bad bands are 30,20,17,12 and 10 meters. Looking at the relay table in appendix B I am not sure which relay could be bad. How can I test them? Should I try to replace them? 73, Keith N8CEP On Mon, Jul 13, 2020 at 4:58 PM Dave Van Wallaghen <d...@w8fgu.com> wrote: > Ok Keith, just to make sure things are where we want on the bands that > seem to work, does the frequency change when turning the VFO knob when > measuring with CAL FCTR on TP1? If they do, then things are working ok. > > For the bands that are locked at 8.28v, that is the max output from the > integrator circuit (U6B). This means that there is no lock between the PLL > Oscillator and the VCO circuit and the PLL chip (U4) is trying to drive the > varactors to provide more capacitance to the VCO circuit. The most likely > cause will be a misplaced capacitor in the VCO range selector (C71 - C75) > or a problem in the VCO circuit itself. But because this may be band > dependent, I would look first in that range selection circuit. Verify that > those caps are the proper values. They are easily misread and will cause > the type of thing you are seeing. > > Also verify those varactor diodes are the proper type and in the right > places. Soldering issues are typically the leading cause of problems, so > check that also. If all looks right to you, you may want to signal trace > through that selection circuit to verify the proper relays and active for > the bands not working. There is a relay table in Appendix B that shows you > which relays are active for each band. > > This is a brand new build, correct? > > 73, > Dave, W8FGU > > > On 7/13/2020 4:41:07 PM, "Keith Hamilton" <n8cep.ke...@gmail.com> wrote: > > Thanks for your help Dave! > > Yes. I was able to get 6 volts on R30 by turning L30. At first the voltage > was too high > so I adjusted the turns on T5 by spreading the red windings further apart. > Then I > was able to get to 6 volts. > > I did a CAL FCTR with the probe on TP1 and the frequency set to 4000, > The reading is 8912.22 > > 73 Keith N8CEP > > > On Mon, Jul 13, 2020 at 3:59 PM Dave Van Wallaghen <d...@w8fgu.com> wrote: > >> Hi Keith, >> >> Were you able to get 6v on R30 by tuning L30? Did you have to bring the >> voltage down or up by moving the windings on T5? >> >> If you would, set the VFO to 4 MHz and do a CAL FCTR on TP1 and let me >> know what the reading is. I'm just looking for a couple of clues before >> we proceed. >> >> 73, >> Dave, W8FGU >> >> >> On 7/13/2020 2:52:11 PM, "Keith Hamilton" <n8cep.ke...@gmail.com> wrote: >> >> >I am having trouble with the K2 VCO alignment. I have moved the T5 >> windings >> >and obtained 6 volts at the left end of R30. I then went on to the chart >> >(table 6-1) to measure the voltages at the listed frequencies. My >> readings >> >are ok on 80 40 and 15 meters (between 1.5 to 7.5 volts) but on 30,20,17 >> >,12 and 10 meters the voltage is 8.29 volts and does not change. >> > >> >I have checked the solder connections of T5 and the value of C72 (271). >> The >> >diodes D21,D22,D23, D24, D25 and D26 are correctly installed. I also went >> >over the solder connections of K13, K14 and K15. >> > >> >Now I'm stuck. Any help will be appreciated. >> > >> >Keioth Hamilton N8CEP >> >______________________________________________________________ >> >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 d...@w8fgu.com >> >> ______________________________________________________________ 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
