[Elecraft] voltage display on K2 -- KB3FBR

[MARY HAYS CARNEY]

Don:

Your email prompted me to make these measurements and clarify my statement about the voltage at D6 and D7:  
The anode voltage at D7 is a zero with key up; however it does not go to 8 v on key down.  The anode at D6 is 7.9 volts with key up (receive) but only drops to about 0.6 v on key down.  I think the problem goes back to U6. I.e. with key up, the voltage on pin 27(TX) of U6 is 0 volts.  On key down, it stays at 0 v.  Thus the base of Q1 (ctrl brd) is not turned on.  At the same time the voltage on pin 28(RX) of U6 remains at 5 volts.    

To complicate things, this behavior is intermittant; on some bands I see the described behavior and on some not, and it even occurs/doesn't occur on a particular band at seemingly random times.  Unless you have the great AHA! with these symptoms you might hold off on a reply until I replace the U6 on the ctrl brd with extra antistatic care and recheck measurements.  Also, I will recheck the low pass filter and T4 before firing it up again.

One more question.  Is there a list somewhere that describes the function of each pin of U6 (ctrl brd)?  For example, I understand the functions of pins 27 and 28, but  don't know which one translates V RFDET to a value for the DAC, U8 as well as functions of pins 21-26.

Thanks,
joe carney KB3FBR