Matthew, Great that you found the source of your problems. Onward and upward.
When you get all finished with your K2 and want to do a good dial calibration, take a look at the K2 Dial Calibration article on my website www.w3fpr.com and you should be able to get it "right on" with that procedure. I do several every week, and I can tell you that the method does work and works quite well. 73, Don W3FPR On 7/17/2012 3:35 PM, Matthew Ellis wrote: > Don, > > Thanks to your pointing me in the right direction I appear to have > tracked down my issue: Capacitor R68 (10pf, next to K15) was duff > (probably damaged when I inserted it as the holes on the pcb are wider > than the lead spacing on the capacitor). The final clue was when I > broke an unrelated capacitor lead off which showed how easily they can > be damaged (I've put hundreds of capacitors into circuits without > issue before), The other clue was that when I touched my frequency > meter probe to TP1 I got a very brief reading before it dropped to > zero, and while it would continue to read zero if I touched tp1 > repeatedly, if I left it for a while (a minute or so) then touched the > probe again, I once again got a brief reading. This suggested to me > that T5 was probably OK (your telling me it was a Hartley oscillator > helped there as I then looked it up to get a better idea of the > operation). > > Lets hope it doesn't take me two weeks to get each of the various > tests to pass! > > Thanks again, > > Matthew > > On 15/07/2012 14:14, Don Wilhelm wrote: >> Matthew. >> >> Zero Hz. says that Q18 is not oscillating. >> To help you visualize a little better, forget about the PLL part and >> concentrate on Q18 only. That is just a Hartley oscillator. >> >> You have already shorted out the VFO ALC with the short across C60 - >> and that is a good debugging step. The tuned circuit inductance >> consists of L30 in parallel with the red winding of T5 and the >> capacitance is made up of the varactors and capacitors switched in >> and out of the circuit by K13, K14 and K15. That is really all there >> is to it as far as basic oscillation is concerned. >> Once it oscillates, then you can consider the other "appendages" like >> the R30 voltage and the VFO ALC. >> >> So, go over the circuit once again with that in mind. There is a >> reason Q18 is not oscillating - Several possibilities: the green >> winding of T5 is wound backwards, the diodes are oriented backwards, >> The varactors are mounted backwards, Q18 is oriented incorrectly, >> Q18 is damaged, >> >> Note also that the path to TP1 includes U3 (which also could be >> failing). Since you have an external frequency counter, check for >> oscillation at the source or Q18 rather than just at TP1. >> >> You should first be trying to just get Q18 to oscillate. Once that >> is working, the other parts come into play to make the frequency of >> oscillation correct. >> >> 73, >> Don W3FPR >> >> >> >> On 7/15/2012 3:44 AM, Matthew Ellis wrote: >>> Hi, >>> >>> I'm struggling to track down an issue with the VCO test in part 2 of >>> the >>> alignment for my K2 (page 64 in my manual). >>> >>> The 4MHz Oscillator calibration looks OK as the frequency on TP3 shows >>> as 12096hz stable (both on the internal test probe and an external freq >>> counter). The PLL test is in range as well. But I get nothing >>> (0hz) on >>> TP1 for the VCO test with both the internal probe and a standalone >>> frequency meter. >>> >>> I've checked and re-wound/re-fitted Transformer 5, gone over my >>> assembly >>> with a magnifying glass a few times (both top and bottom side of the >>> pcb), confirmed all the components in the VCO area are present and >>> correctly oriented. I've also used a signal scanner on the i2c >>> lines to >>> confirm the pll ic is getting the 'change freq' instructions. Most >>> voltages appear good compared to the manual, although the voltage on >>> Q16 >>> C and Q17 G is off (initially 8v then dropped to near 0v after i >>> re-soldered the joints of resistor R9). I have shorted C60 to >>> completely bypass the VFO ALC (suggestion from Elecraft). >>> >>> All prior tests were fine, everything in expected range. Also the >>> correct frequency shows on pins 1 and 2 of U4 (MC145170), and voltages >>> look good on U3,4 & 6. >>> >>> I'm in the UK, so sending it back to Elecraft is not my preferred >>> option >>> (time/cost). >>> >>> Has anyone got experience of issues in this area? >>> >>> Thanks, >>> >>> >> > > ______________________________________________________________ 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
