[Elecraft] K2 U10C Oscillating

[DAVID POWELL]

On my K2 (#3014) I hear signals and noises while tuning across 160m with the antenna disconnected. The worst is a strong but unstable signal that moves from about 1850 kHz to about 1910 kHz during about 15 minutes after I switch on the radio. I accidentally traced the signal to U10C on the control board: the signal jumped when my finger got near the left end of resistor pack RP2. (U10C appears to be a buffer for the V BIAS-XFIL line.) 

The signal is several kHz wide and resembles hash from a dimmer or switching power supply.

I have verified the U10 circuit resistors and voltages as nominally correct.

U10D, an identical circuit for the V BFO line has pretty clean dc at its output.

Has anyone else seen this? Am I correct in concluding that I should replace U10?

73,
David, NM5U