[Elecraft] K2 PLL calibration

[DHK2BOB@aol.com]

Thanks for the help so far.  I wonder if you might look at this again. 

I have checked resistance and voltage measurements along the new circuit 
board that replaces RP3 as part of the PLL upgrade mod.   All is good as compared 
with a working rig owned by K3IU.

W3fpr suggested that there may be something wrong with pins 1, 2, and 3 of 
U5.   (which in turn seems to be controlled by U4)  I measured these pins with 
the volt meter but I am not sure that this is a good test.  Nevertheless pin 1 
starts at 5 volts and stays at 5 volts whether or not band plus or band minus 
is pressed. Pin 2 starts at 0 volts and then goes to 5 volts when either plus 
or minus is pushed. But only for a half second. 

Pin 3 is 5 volts all the time.  Pin 4 starts at 5 volts and stays there when 
band plus is pushed but briefly drops to 3 volts when band minus is pushed. 

For what it's worth, there is S meter activity when in CAL FCTR.    I do have 
the probe in TP3.  Rev A board    SN142.

It appears that the band up and down switch is "dirty" and not always making 
a good contact. This isn't true since the band changes are positive both up 
and down.  However, the symptoms when measuring the PLL freq. are "mushy" 
switches. The voltage change doesn't always take place at the same pace and the 
changed voltage isn't always the same value.  Sometimes it is 0 volts and 
sometimes 1.3, etc.  Naturally this could be due to that fact that the digital meter 
isn't registering quickly enough as the voltage change is only for a half a 
second. 

Do any of you know how this control circuit works?  What causes the button 
push to hold the setting and what releases it?  Perhaps there is junk on the 
control signal which is causing the latch to let go of the state that the band 
switch puts it in.  

Thanks for your thoughts. 

73,
Bob WB2DHK


--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---