[Elecraft] K2 PLL calibration

[Masleid, Michael A.]

Hi Bob,

The voltage that you see at U5 seem reasonable.  The 3 volts at pin 4
is odd, but since this represents a high speed digital signal, it might
show up as any value between 0 and 5 for a short time.

As to how the circuit works:

The LTC1451 contains a shift register.  "Ones" and "Zero" are sent to =
pin 2,
and clocked into the shift register with clock pulses on pin 1.  Other =
data
and clock is sent to other chips the same way, so you will see a lot of =
junk
on pin 1 and pin 2 that is being used elsewhere.  The LTC1451 only =
responds
to stuff on pin 1 and pin 2 when pin 3 is held low, that is, DAC2CS is =
at
zero volts.  This happens once in CAL FCTR each time you hit BAND+ or =
BAND-.
The data that is shifted into the LTC1451 is latched on the output when
DAC2CS goes high again.  The data will be "remembered" as long the 5 =
Volt
power supply voltage is not disturbed, and as long as there are no =
"glitches"
on pin 3.  The quickest way to get a glitch on pin 3 is to touch the VFO
knob.  It turns out that the LTC1451 gets loaded with new data when you
change the VCO setting.  If you spin the knob, you should see a very =
steady
pulse on pin 3, and you can see the data pattern counting through values
on pin 2 (using a 'scope of course).  So.... if there is something wrong
with your shaft encoder or VFO knob felt washer, that could cause some =
of
the trouble you are seeing.

If you put the rig in CAL FCTR with the probe at TP3, you should be able =
to
see the frequency cycling through a short range of frequencies as you
rotate the VFO knob.  You should also see a slight dip in voltage at
pin 3 if you spin the knob fast....

Do you have access to a scope with triggered sweep capability, or
access to a digital pulse catcher?  You need to see if there is one and
only one pulse at pin 3 for each push of BAND+ and for each push of =
BAND-.

Good luck and 73, Michael, AB9GV