I'm back.... I got the new components (D16, D17, C84, C85, & Q19) from Scott over at Elecraft and installed them. I still got the same readings so I re-read the instructions and checked each and every component to make sure that I had everything installed correctly.
I did find one mistake, I had soldered C88 to pins 11 & 12 of U4 instead of pins 12 & 13. I relocated the cap and the frequency went up slightly (reading 524 instead of 495). The cap measured ~58 picos (in circuit) so it's in the ballpark. I also touched up a few soldering joints along the way, more for looks than anything else. The voltage readings on pins 1, 2, & 3 of U6 are the same as before, and both variactors seem to be working just fine. Any ideas? Thanks again for all of your help, John > > From: "Don Wilhelm" <[EMAIL PROTECTED]> > Date: 2006/04/11 Tue PM 08:18:46 CDT > To: <[EMAIL PROTECTED]>, > <[email protected]> > Subject: RE: [Elecraft] K2 Alignment & Test, Part II PLL problem, Continued > > John, > > For the time being (until you solve the current problem) the only voltages > at U6 that matter are pins 1, 2 and 3 - and those are correct. The other > pins will likely fall into line after you have this problem fixed and if not > there is another problem with the VCO. > > Right now, the voltages being fed out of U6 pin 1 are correct for the > stimulus you provided (CAL FCTR and tapping BAND+ and BAND-). Now check to > see if that (proper) 0 to 8 volt swing between pressing BAND+ and BAND- is > carried on through R19 and then through the RP2 sections and then onto the > cathodes of D16 and D17. If you get a decent voltage swing between BAND+ > and BAND- (you can expect a bit of voltage drop on the 8 volts end) at the > varactor cathodes, then look for something else wrong in the PLL Reference > oscillator (upper left of the schematic sheet - but only as far to the right > as TP3), the PLL chip does not matter until the PLL Reference oscillator is > functioning properly. > > If you do get a good voltage swing at the varactors, then all I can say is > either Q19 oscillations quit when the varactor capacitance is reduced, or > there is something wrong at C84, C85, D17 or D16 which is stopping the > oscillation. If you suspect Q19 itself, you could try swapping it with one > of the J310s on the Control Board at Q6 or Q7 (these in a less-critical > audio circuit rather than being used as an RF Oscillator). > > 73, > Don W3FPR > > > -----Original Message----- > > > > Thanks for the help Don. :) > > > > I tried your suggestions (and a few others as well) and L31 > > (which is a 12 µHz inductor on my unit) is the correct part. > > > > Diodes D16, D17, & D18, are in properly and pass their in-circuit > > tests just fine. > > > > R19, RP2, R20, R21, RFC14, C84, C85, Q19, RFC14, Q19 and the > > thermistor board are all installed properly and certainly look good. > > > > > > Scott at Elecraft suggested holding the 4, 5, & 6 buttons while > > turning the unit on (which showed "INFO 201") to see if that > > corrected the problem but no luck there either. > > > > I took reading off of U6 while switching between "BAND -" and > > "BAND +" in "CAL FCTR" mode, and here's what I got: > > > > BAND +, The display reads 488Hz (Bad) > > > > U6 Readings: > > Pin 1 = 7.63V > > Pin 2 = 4.09V > > Pin 3 = 4.09V > > Pin 4 = 0V > > Pin 5 = 3.96V > > Pin 6 = 4.91V > > Pin 7 = .02V > > Pin 8 = 7.95V > > > > > > BAND -, The display reads 12086Hz (Good) > > > > U6 Readings: > > Pin 1 = .00V > > Pin 2 = .09V > > Pin 3 = .02 > > Pin 4 = 0V > > Pin 5 = 3.96V > > Pin 6 = 3.96V > > Pin 7 = 1.64V > > Pin 8 = 7.95V > > > > > > Pins 2, 3, 6, especially Pin 6, are out of tolerance. > > > > Taking resistance readings off of the thermistor board looks good. > > > > Pins 6/7 to Pin 8 reads about 5k ohms. > > Pins 4/5 to Pin 8 reads about 295 ohms. > > Pins 2/3 to Pins 4/5 reads about 1.96k ohms. > > Pins 6/7 to Pin 1 reads about 8.76k ohms. > > Pin 1 to Pins 2/3 reads about 1.8k ohms. > > > > All of these readings more or less mathematically work out to > > what the meter says (with the exception of the second reading > > which is 8V to Ground so no surprise there). > > > > The output from the DAC is 4.092 (4,092 counts), so it's near its > > top end. > > > > > > My partner suggests removing R19 and inserting a pot to swing the > > voltage going into the oscillator circuit from 0 to 7-ish volts > > to see if that stabilizes. > > > > > > I got another suggestion to double check D36 for proper > > installation. It's in correctly, and checks out (in circuit) okay. > > > > Possibly I left a component out, so I'll double check that I > > didn't skip anything during the installation phase. > > > > > > Thanks again for all the help, > > > > John > > > > > > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
