[Elecraft] K2 U10a on control board oscillates on receive

[Marshall Jose]

My K2's ALC circuit on the control board oscillates at around 50 Hz 
during receive. During receive, the "V PWR" voltage is set to zero, so 
maybe there's some instability associated with driving U10a into its 
non-linear region.

At any rate, it has no effect on receive operation since the BFO buffer 
the "V ALC" signal controls is effectively blocked further down the xmit 
signal path. But I've noticed that it can cause trouble because when 
it's in that state it won't re-enter a linear mode until the power 
control is increased during xmit above a certain level.

And I've noticed some rather severe limitations on the power I can 
transmit in the higher bands, and have wondered about the words in the 
troubleshooting section: "If you have seen a slow (10-20Hz) oscillation 
superimposed on the transmitter's output signal, it could be due to ALC 
modulation. Increase the value of R98 (RF board) to the largest size 
that permits full output on 10 m."

Has anyone seen this behavior? Can anyone suggest a course of action? I 
have a full suite of RF test equipment, so I can chase a signal through 
the whole unit if necessary.

Thanks,

-- 
Marshall Jose, WA3VPZ