K2 Alignment and Test Part II: VCO Test fails

Posted by Matthew Ellis on Jul 15, 2012; 7:44am
URL: http://elecraft.85.s1.nabble.com/K2-Alignment-and-Test-Part-II-VCO-Test-fails-tp7559122.html

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,


Matthew

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