[Elecraft] K2 no transmit, and no sidetone

[James T. "Jim" Rogers]

Bill wrote:
I'm working on K2 serial 2862 for a friend.  He recently replaced P4 on the
control board, and cleaned up some errors in wiring the mic configuration.
Up to that time the K2 was working fine; being used solely on PSK-31.  The
unit is the QRP version with SSB board, battery and no other options.

When I received # 2862 there was no transmit on CW or SSB, and there was no
sidetone/spot tone.  There's no spot tone at the output of contol board U6,
and I suspect this has someting to do with no RF output.

The unit draws 2.5 amps (possibly more) key down, but does not produce RF
output. All resistance checks are good for the RF amp section and the
driver.

The receiver is working fine on 40M, and the alignment and signal tracing on
the receive path looks OK.

Not knowing the logic of the control board U6 and other chip components, I
can't tell what their function is supposed to be, so can't trace any logic
through them.

Any ideas on what might be wrong, and what to check?

Bill, I am just looking for something common between sidetone and the rf
section. What I came up with is the 8.0V supply which basically comes from
an LM2930 on the Control Board.
If I can answer any questions you have on the logic of the control board (I
have on occassion experienced a difficulty or two there) please let me know.

Boy what a shot in the dark, but one never knows.....
73, Jim W4ATK
K2 #4028
j.t.rogers@charter.net