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
