PLL Reference Oscillator Question
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Hello everyone. I purchased my K2 kit about 4 years ago and as life would
have it, I rarely have time to work on the beast except during holidays etc. More time for amateur radio would sure be nice, but I'm not near retirement and for some reason I keep getting pesky bills in the mail. Anyway here is my situation: 1) I am at the Alignment and Test, Part II portion and trying to get through the 4 MHz Oscillator Calibration section. 2) When I take a freq. measurement at TP3 for the PLL with the frequency probe, I get a reading of ~12650, obviously way too high. 3) I inspected parts, soldering etc and cannot find a fault. 4) Decided to do some signal tracing and performed a measurement of the reference oscillator signal on pin 1 of U4. My reading is .51, instead of the expected 0.8-1.8. Vrms. So my question is this: It seems that the 12650 measurement is so high that it may be an indicator that the X1 crystal in the PLL oscillator is defective. However, with the low reading on pin 1 of U4 I'm not so sure about the crystal. Could the increased frequency reading at TP3, cause the voltage drain on the U4 or am I barking up the wrong tree? I've looked through the email archives and haven't found anything quite similar to my issue. I hate to start pulling stuff apart if the crystal is the issue and would like to hear what others think of the problem. Thanks, 73 and Happy Holidays! Byron Viets N6UI ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: PLL Reference Oscillator Question
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Byron,
Don't be too concerned about the 4 MHz oscillator calibration at this point in your assembly process. Once you have completed your K2, you can refine the calibration - see the K2 Dial Calibration article on my website www.w3fpr.com for "the rest of the story". Yes, 12650 is higher than the high end of the range should be, but please tell me what the low range is - while in CAL FCTR, tap BAND+ and tell me what the frequency is, then tap BAND- and again tell me what the displayed frequency is. Perhaps I can craft an answer to the possible trouble spots from that information. 73, Don W3FPR Byron Viets wrote: > Hello everyone. I purchased my K2 kit about 4 years ago and as life would > have it, I rarely have time to work on the beast except during holidays etc. > More time for amateur radio would sure be nice, but I'm not near retirement > and for some reason I keep getting pesky bills in the mail. Anyway here is > my situation: > > 1) I am at the Alignment and Test, Part II portion and trying to get through > the 4 MHz Oscillator Calibration section. > 2) When I take a freq. measurement at TP3 for the PLL with the frequency > probe, I get a reading of ~12650, obviously way too high. > 3) I inspected parts, soldering etc and cannot find a fault. > 4) Decided to do some signal tracing and performed a measurement of the > reference oscillator signal on pin 1 of U4. My reading is .51, instead of > the expected 0.8-1.8. Vrms. > > So my question is this: > > It seems that the 12650 measurement is so high that it may be an indicator > that the X1 crystal in the PLL oscillator is defective. However, with the > low reading on pin 1 of U4 I'm not so sure about the crystal. Could the > increased frequency reading at TP3, cause the voltage drain on the U4 or am > I barking up the wrong tree? > > I've looked through the email archives and haven't found anything quite > similar to my issue. I hate to start pulling stuff apart if the crystal is > the issue and would like to hear what others think of the problem. > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Hi Don,
Thank you for your response. When I try the freq. range test, there is no freq. change. I searched the reflector and found an earlier email response authored by yourself with the subject of: K2 PLL range test SN 05233. That person had a similar issue, so it would seem I can start tracking down the problem based on your diagnosis in that email. 73, Byron N6UI
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Re: PLL Reference Oscillator Question
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Byron,
Yes, that prior response may be helpful, but all may not apply to your case - each one is different. To be specific for your problem, first monitor the voltage from RF Board U5 pin 7 while in CAL FCTR mode. When tapping BAND+, the voltage should go to about 4 volts and tapping BAND- should drop the voltage to near zero volts. If that is OK, then move on to U6 pin 1 - tapping BAND+ should produce about 8 volts and BAND- should produce nearly zero volts. Check those conditions first. If those are all OK, then you can move on to the varactor tests, but if there is a problem with the voltages above, get back with me for additional tests and actions. 73, Don W3FPR bviets wrote: > Hi Don, > Thank you for your response. When I try the freq. range test, there is no > freq. change. I searched the reflector and found an earlier email response > authored by yourself with the subject of: K2 PLL range test SN 05233. That > person had a similar issue, so it would seem I can start tracking down the > problem based on your diagnosis in that email. > 73, > Byron > N6UI > > > > Don Wilhelm-4 wrote: > >> Byron, >> >> Don't be too concerned about the 4 MHz oscillator calibration at this >> point in your assembly process. Once you have completed your K2, you >> can refine the calibration - see the K2 Dial Calibration article on my >> website www.w3fpr.com for "the rest of the story". >> >> Yes, 12650 is higher than the high end of the range should be, but >> please tell me what the low range is - while in CAL FCTR, tap BAND+ and >> tell me what the frequency is, then tap BAND- and again tell me what the >> displayed frequency is. Perhaps I can craft an answer to the possible >> trouble spots from that information. >> >> 73, >> Don W3FPR >> >> Byron Viets wrote: >> >>> Hello everyone. I purchased my K2 kit about 4 years ago and as life >>> would >>> have it, I rarely have time to work on the beast except during holidays >>> etc. >>> More time for amateur radio would sure be nice, but I'm not near >>> retirement >>> and for some reason I keep getting pesky bills in the mail. Anyway here >>> is >>> my situation: >>> >>> 1) I am at the Alignment and Test, Part II portion and trying to get >>> through >>> the 4 MHz Oscillator Calibration section. >>> 2) When I take a freq. measurement at TP3 for the PLL with the frequency >>> probe, I get a reading of ~12650, obviously way too high. >>> 3) I inspected parts, soldering etc and cannot find a fault. >>> 4) Decided to do some signal tracing and performed a measurement of the >>> reference oscillator signal on pin 1 of U4. My reading is .51, instead >>> of >>> the expected 0.8-1.8. Vrms. >>> >>> So my question is this: >>> >>> It seems that the 12650 measurement is so high that it may be an >>> indicator >>> that the X1 crystal in the PLL oscillator is defective. However, with the >>> low reading on pin 1 of U4 I'm not so sure about the crystal. Could the >>> increased frequency reading at TP3, cause the voltage drain on the U4 or >>> am >>> I barking up the wrong tree? >>> >>> I've looked through the email archives and haven't found anything quite >>> similar to my issue. I hate to start pulling stuff apart if the crystal >>> is >>> the issue and would like to hear what others think of the problem. >>> >>> >>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[hidden email] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> >> >> > > > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.722 / Virus Database: 270.14.120/2587 - Release Date: 12/26/09 03:27:00 > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Don,
I did the voltage tests and they both checked out. U6 was at 7.4, so a little under 8, but I would imagine that is within tolerance. 73, Byron N6UI
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Don,
I also took the liberty to do the checks on: RP2 pin 2, and the cathodes on D16 and D17 and they all behaved like U6 pin 1: 7.4 and zero when switching between BAND+ and BAND-. 73, Byron N6UI
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Re: PLL Reference Oscillator Question
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Byron,
Fine on all that, so far so good - next is to check L31, X1, R21, D18, C84 and C85 for good soldering, and make certain D16 and D17 are oriented correctly. If nothing is found awry, I would arbitrarily replace X1 as the first step and after than D16 and D17. Remember that this is just like a VXO circuit, no real 'magic', you add capacitance (that is what the varactors should be doing at lower voltages) and the frequency shifts downward. 73, Don W3FPR bviets wrote: > Don, > I also took the liberty to do the checks on: RP2 pin 2, and the cathodes on > D16 and D17 and they all behaved like U6 pin 1: 7.4 and zero when switching > between BAND+ and BAND-. > 73, > Byron > N6UI > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Don,
Well everything checked out, i can't find any fault with the installation of those components. Looks like I need to order some parts, unless you can think of anything else I should check. If I haven't mentioned it, thank you for all of your help and attention. 73, Byron N6UI
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Hello Don,
Hope you had a good New Year's. I replaced X1 and subsequently D16 and D17, with no luck, still reading 12650. Getting a little frustrated. Any suggestions? 73, Byron N6UI
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