[Elecraft] [K2] Sidetone has suddenly disappeared.

[Chip Stratton]

My K2 suddenly quit supplying a sidetone. Changing sidetone level and
frequency do nothing.

Per the troubleshooting guide, I've found that the drain of Q5 has no AC
voltage when key down, while pin one of U10 (IIRC) is supplying 5 volts (and
pin 25 of the IC in the previous step had expected 2.5v AC).

So, this seems to mean that Q5 is bad, but when I pulled it and tested it
with the M3 semiconductor analyzer, it is not obviously bad (to me anyway).
It reads NMOS Vth=1.76v, S-G-D mA=1.13  - whatever that means, I don't know
enough to interpret.

Any off the cuff ideas? I have a replacement 2n7000 on the way, but still
wondering why it would fail in circuit, and if its really bad.

Thanks,
Chip
AE5KA