[Elecraft] K2 RF Gain Control Quit

[N2EY@aol.com]

Folks,

K2 #2084 (Rev. A, no mods) has developed some strange symptoms over the past few days....

When first turned on, only the very strongest signals can be heard, S meter is fullscale and RF gain control makes no difference. Rx acts as if RF gain is turned way down. Turning AGC on or off doesn't help.

Tap the key and after each dit or dah the gain jumps up to normal for a couple of milliseconds, then drops back to very low gain.

After some time, rx begins to act normally, but the response to the RF gain control is very slow (turn the knob and the RFG goes up or down very slowly).

Symptoms come and go.

Looking at the schematic, it appears to me that the PN2222 transistor, 1N4148 diode and 3.3 meg resistor in the AGC circuit are prime suspects. 

As I understand the circuit, the two op amps (U2) have pretty close to unity gain, and are used mostly for isolation and to drive the various control lines. The PN2222 is an emitter follower which charges the AGC time constant capacitors and provides T/R control. The 3.3 meg resistor gives the AGC time constant caps a predictable decay time.

Any hints or suggestions before I start poking about? Firstordr of business seems to be voltage checks.

73 de Jim, N2EY

After some time,