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
