[Elecraft] K2 BFO problem, need JFET advice

[Don Wilhelm]

  Tyler,

Since you have low audio output during receive, I would suggest you are 
looking in the wrong place.
Q24 is not involved during receive, and will show no signal at TP2 
during receive.

The 400 mV at the gate of Q24 is just fine.  Put the K2 menu into CAL 
FCTR and then check the RF level at TP2 - it should be somewhere between 
25 and 70 millivolts.

You may be in for some Signal Tracing.  Use the steps found in Appendix 
E of the manual.

On 7/1/2011 10:45 AM, Tyler Barnett wrote:
> Symptom:
>
> K2 with very low audio output, only the strongest stations can be copied.
> Have eliminated the BPF, attenuator, pre-amp, and so forth with signal tracing.
> Transmit stops increasing at about 4W, the control runs out of effect.
> So the K2 is alive, but something is wrong in the signal path.
>
> The BFO area was redone with a mod (which I have no paperwork on, somebody else's radio).
> The components were dead-bugged onto the area around the T33 BFO toroid, and I believe they shorted out on the bottom cover.
> Using the included kit RF probe, test point TP2 has only 1 millivolt on it, but Q24 has about 0.4Vrms on the gate, which is fed from U11 pin 6 and through the BFO components.
>
> Thus, it appears to be a blown Q24, which is a JFET  J310.
> Radio Shack has a MPF102, would that be OK to use?
> I've checked the respective datasheets of J310 vs MPF102, and I haven't found much difference in ratings, even the noise figure is about the same.
>
> Your comments appreciated ASAP!
>
>