[Elecraft] K2 VCO Alignment only 0.02V @ R30

[JeremyJones]

So this morning I started rechecking everything.  I've found that the 5V on
U4 pin 5 is intermittent.  Not in a way that would indicate a loose or poor
connection, but either that it is there, or it isn't (mostly isn't) when
powering up the unit.  U7 always has the 5V on pin2.  I checked the
resistance between U7 pin2 and U4 pin 5 and found about 300k.  Looking at
the schematics however, it looks like U4 pin5 is actually connected to U7
pin5 (SDO).  There is less than 1 ohm of resistance between U4 pin5 and U7
pin5, so it would appear that U7 may have an issue.

The other odd thing is that even when there is 5V coming into U4 pin5, the
symptoms at R30 (0.020V) and the low band frequencies are still there.  It
looks like U7 may provide U4 a clock signal as well.

I was seeing the 8V at R30 after reflowing all of the joints near the PLL
Reference.  Could the increase in temperature in the are have triggered the
thermistor?

The only thing changed between having the 8V at R30 last night and then
losing it was the rewinding of T5 to bring it back up to 16 turns of red. 
The continuity checks are good through it, and L30 still changes the
frequency when adjusted.



--
View this message in context: http://elecraft.365791.n2.nabble.com/K2-VCO-Alignment-only-0-02V-R30-tp7569523p7569573.html
Sent from the Elecraft mailing list archive at Nabble.com.