[Elecraft] RE: K2 VCO Testing problem

Sat Nov 22 15:57:04 EST 2008

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 0.6-0.75VDC measurements :Q18G     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, 73Marinos, sv9dru / ki4gin> Subject: Welcome to the "Elecraft" mailing list> From: elecraft-request at mailman.qth.net> To: sv9dru at hotmail.com> Date: Sat, 22 Nov 2008 15:58:05 -0500> > Welcome to the Elecraft at mailman.qth.net mailing list!> > To post to this list, send your email to:> > elecraft at mailman.qth.net> > General information about the mailing list is at:> > http://mailman.qth.net/mailman/listinfo/elecraft> > If you ever want to unsubscribe or change your options (eg, switch to> or from digest mode, change your password, etc.), visit your> subscription page at:> > http://mailman.qth.net/mailman/options/elecraft/sv9dru%40hotmail.com> > You can also make such adjustments via email by sending a message to:> > Elecraft-request at mailman.qth.net> > with the word `help' in the subject or body (don't include the> quotes), and you will get back a message with instructions.> > You must know your password to change your options (including changing> the password, itself) or to unsubscribe. It is:> > 7795> > Normally, Mailman will remind you of your mailman.qth.net mailing list> passwords once every month, although you can disable this if you> prefer. This reminder will also include instructions on how to> unsubscribe or change your account options. There is also a button on> your options page that will email your current password to you.
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