OK Dave - I will check the relays as you suggest. In troubleshooting capacitors I messed up C74. I pulled it off the board and sent a request to Elecraft for a replacement. That may solve the problem. In the meantime I will check the coils on the K13 to K15 relays and let you know what I find.
I did not see Don's post. I will check it out. So I will be waiting a bit to fix this problem, 73 and thanks! Keith N8CEP On Mon, Jul 13, 2020 at 10:36 PM Dave Van Wallaghen <[email protected]> wrote: > Keith, > > I saw Don respond to this and he is right that K15 would be the common > denominator if not for 15m. You can check to see if the coils are intact > if you measure the resistance between pins 1 and 10 for each. It should > be around 230 ohms or so. If you find one open or well away from that > resistance, then it would indicate a bad coil on that relay. > > You can also measure the intended path through the relays for each band > and make sure there are no unintended paths. If you can read the > schematic, it shows the path with each relay in it's reset state. You > would need to consult the table in Appendix B to see which relay(s) are > active for a respective band and you can then measure the continuity of > the intended path. You should also check any unintended paths which > could indicate a problem. > > As Don stated, this is not a fun problem to find and will take some good > debugging skills. So far, everything you've indicated seems to suggest > the PLL oscillator and VCO circuits are working properly, but the range > selection area is not producing the proper capacitance to allow the VCO > to produce the proper frequency on those bands you indicated. > > If reading the schematic is a problem, let us know and I am sure between > Don and myself, we can give you some step by step instructions for > tracing through this problem. > > 73, > Dave W8FGU > > ------ Original Message ------ > From: "Keith Hamilton" <[email protected]> > To: [email protected] > Sent: 7/13/2020 9:34:03 PM > Subject: [Elecraft] Fwd: Re[2]: K2 7747 VCO alignment problem > > >---------- Forwarded message --------- > >From: Keith Hamilton <[email protected]> > >Date: Mon, Jul 13, 2020 at 9:19 PM > >Subject: Re: Re[2]: [Elecraft] K2 7747 VCO alignment problem > >To: Dave Van Wallaghen <[email protected]> > > > > > >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 <[email protected]> > 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" <[email protected]> > 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 <[email protected]> > 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" <[email protected]> > 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:[email protected] > >>> > > >>> >This list hosted by: http://www.qsl.net > >>> >Please help support this email list: http://www.qsl.net/donate.html > >>> >Message delivered to [email protected] > >>> > >>> > >______________________________________________________________ > >Elecraft mailing list > >Home: http://mailman.qth.net/mailman/listinfo/elecraft > >Help: http://mailman.qth.net/mmfaq.htm > >Post: mailto:[email protected] > > > >This list hosted by: http://www.qsl.net > >Please help support this email list: http://www.qsl.net/donate.html > >Message delivered to [email protected] > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
