[Elecraft] PLL calibration

[Masleid, Michael A.]

Hi Bob,

>I just did the BFO mod and the PLL mods.  Ran CAL PLL and nothing =
happens. =20
>Shows 12.092 MHz and nothing else. No little "ds" flashing.  Waited for =
15=20
>minutes, no beep. =20

>However - when checking PLL range by pushing the band+ and band- there =
is=20
>only a quick blip of the higher or lower frequency - then it reverts to =
the 12=20
>MHz number - almost too fast to see, but the range is within specs. =20

The PLL mod changes how U6A works, a little bit.  Normally, if U5 pin 7
puts out 0 volts, U6A will put out 0 volts.  If U5 pin 7 puts out 4 =
volts,
U6A will put out 8 volts.  So U6A is just an amplifier with a gain of 2.

That voltage should get to C100, and control D16 and D17.  It sounds =
like
something is happening in your circuit that allows a fast change to make
it to C100, but slower changes (from U5 pin 7) are not making it =
through.

I can't see a simple way for this to happen.  If you replaced R19 with a
capacitor??

I think I'd put a voltmeter on U5 pin 7, and at U6 pin 1 (one end of =
R19),
and on C100 (the other end of R19), then do the PLL range check and make =
sure
that the voltages out of U5 pin 7 make it all the way to C100.  Figure =
that
U5 pin 7 should switch between 0 and 4 volts when you do the range =
check,
and it should ramp between those voltages with CAL PLL.  Make sure the
voltage at C100 can track those changes.  If not, find out where the =
signal
went away.

73, de Masleid, AB9GV