Hi, That makes sense. I assume this is a bootstrap problem then i.e. the J310 has to be oscillating in the default state before the VCO linearisation can run and set up the LUT inside the EEPROM. Making a large assumption there of course as I can't see the source code!
I tried the 10pF trick from another thread that you mentioned before after researching this issue and unfortunately that didn't start the oscillation. I did some experiments and will complete one more: Experiment 1 .... Did a hard reset (456+power up) to see if it reset the data. It showed the initialisation info message. FAIL Experiment 2 .... I just checked the VXO range by pulling R19 and using another bench supply. The thing gives a relatively reliable 3v p-p until the varactor control voltage hits 6.8V then it stalls. Obviously as DAC output eventually ends up at 7.07V it's game over straight up. Experiment 3 .... If I leave R19 lifted and run the PLL cal it doesn't throw info 232 straight away but appears to hang, probably because there's no control voltage doing anything which is hopeful if it works how I think it does! Experiment 4 .... (in progress) I'm going to put a J309 in (I don't have any spare J310s I don't think and this is same FET but binned with different Idss) and see if it oscillates across the full range. I will then run PLL cal. If that works then it'll at least clarify first assumption. I checked /DAC2CS and it does indeed go low during the load operation. The issue is the control data sent to the DAC is the same. Thanks for your help. Some ideas to try! Best regards, Chris On Tue, 21 May 2019, at 19:05, Don Wilhelm wrote: > Chris, > > If your kit was shipped between mid-August 2018 and mid-January 2019, > then the most likely problem is that Q19 should be replaced with a new > J310 from Elecraft. > > As for the 7.07 volts from U6A pin 1, that is not necessarily the cause > of the problem (Q19 should oscillate even with almost 8 volts from U6 > pin 1) - if it does not, then the problem is Q19. > > While waiting for a replacement J310 from Elecraft, try putting a small > value capacitor from the source of Q19 to ground - use 10 to 15pF. Then > measure the PLL Reference oscillator range using the counter probe in > TP3 and entering CAL FCTR in the menu. You should have oscillation at > both the low (BAND-) and high (BAND+) and the frequency of the high end > should be near 12100 kHz. > > Another potential problem if the voltage on U5 pin 7 (and as a result U6 > pin 1) can be that the /DAC2CS input to U5 pin 3 is always at or near > ground - check for that condition, and if present, find the solder > bridge. That signal line should go to ground as you rotate the VFO, but > otherwise should be at 5 volts. You will need an oscilloscope to see > the negative transitions. > > 73, > Don W3FPR > > On 5/21/2019 12:27 PM, Chris Smith wrote: > > Hi, > > > > I've just completed my K2 up to the PLL reference oscillator. > > > > Initially when I assembled it the PLL reference oscillator would not > > oscillate at all. No reading on internal counter. I popped it on my > > external Racal counter and still dead. After tracing the problem out I > > found that the voltage on input to the varactors was pegged at 7.07V which > > was too high for the oscillation to carry on. I lifted one end of R19 on > > the output of U6A and the thing oscillates fine isolating this to a control > > voltage problem. > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
