[Elecraft] RE: K2 VCO Testing problem the stupidity factor...

Sun Nov 23 05:14:09 EST 2008

False alarm guys,
I was stupid enough to have D13 installed backwards !! After returning it to its proper orientation, everything is back to normal. Fortunately enough I did not engage in any heroic desoldering action attempts (relays, ICs etc) before I see the cause of the VCO problem....

Just an advice for the avid builders: When you feel tired, take a break...there is a good reason for feeling tired, do not ignore it. It is like feeling "OK" to drive after having a couple (or more) drinks!!

73 to all,
Marinos, sv9dru/ki4gin> Date: Sat, 22 Nov 2008 19:40:35 -0500> From: w3fpr at embarqmail.com> To: sv9dru at hotmail.com> CC: elecraft at mailman.qth.net> Subject: Re: [Elecraft] RE: K2 VCO Testing problem> > Marinos,> > Marinos,> > Based on your voltage readings at Q18, the VCO is not actually > oscillating (indicated by a lack of negative voltage at the gate). I > don't know why you have any frequency reading at TP1, but I would tend > to disregard it for the moment.> > The first thing to check is the orientation of D13 and D8. If those are > OK, I would try replacing Q18.> All other components connected to Q18 are suspect, so check all of them > for correct values.> > Q17 could also be at fault - check it quickly by placing a short from > the drain to the source and see if you get a negative voltage on the > gate of Q18 - if so, Q17 should be replaced.> > Also, check the soldering at relays K13, K14 and K15 and the value of > C72. Check the varactors D21 through D26 to be certain they are the > correct type and oriented properly.> > 73,> Don W3FPR> > 73,> Don W3FPR> > Marinos Markomanolakis, M.D. wrote:> > Dear Friends,> > I am in the process of building my serial# 6614 K2 (the 3rd one that I > > have built since 2000), and run into a problem during the VCO testing: > > First, the PLL reference Oscillator test checked within specs, but in > > the next (VCO) test, while checking at TP1 with the frequency > > counter,with the K2 at 4.000.10Khz, I am measuring a 7.59 to 7.60Mhz > > with the last digits of the reading rapidly alternating.> > The DC voltage at the left end of R30 is about 5.3V with some > > spontaneous fluctuation, and not responding to adjustment of the L30 > > as per the VCO alignment test in page 64 of the manual.> > Reheating the leads of T5, checking C72 and general check for > > soldering issues did not reveal anything.> > > > PLL reference oscillator output with the RF probe: Pin 1 of U4 1.08V > > (ok), but VCO output signal (pin 3 of U3) 1.13V when only 0.3-0.4V are > > acceptable and VCO buffer output (pin 6 of U6) 0.85V with the > > acceptable range being 0.6-0.75V> > DC measurements :> > Q18> > G 0.0V (-1.0)> > S 4.3V (2-3)> > D 7.1V (6.3)> > U3 Pin#> > 1 1,1V (0.0)> > 2 3.9V (4.3)> > 3 3.8V (4.1)> > > > U4 Pin#> > 3 3.5V (0.0)> > 7 5.0V (0.0)> > 8 0.06V (0.1)> > > > The values in the parentheses are the acceptable per the manual, and > > the rest of the IC pins are within specs.> > > > Based on the above, I suspect that for some reason the U4 IC might be > > the problem (eventhough I did observe antistatic and overheating > > precautions), but since its replacement can be technically difficult > > and would have to be posponed until the part arrives from Elecraft to > > the SV1 land, I would like to have your opinion as to how I can > > further troubleshoot this problem before starting changing parts etc.> > > > Thanks, 73> > Marinos, sv9dru / ki4gin> >
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