[Elecraft] K2/100 Fault finding

[Michael Carter]

Hi Steve,

The absence of the high voltage reverse bias supply on the cathodes of D12 and D14 when in TX key-down state suggests two possibilities

  1.


  1.
Q6 has failed with a permanent drain-to-source short. That would provide a path for current through D14 as well as through D13 when in transmit mode for power settings above 10 watts.
  2.
The high voltage bias supply has failed.  This is easily checked by measuring the DC voltage at the junction of R11 (510k) and C77 (0.015 uF).

Please let us know what you find.  If your old transistor tester is designed to test NMOS FETs, I would be surprised.  It's best to just measure the drain voltage of Q6, first in RX mode, then in TX mode.  Be sure the transmit power control is set above 10 watts to engage the PA module.  In RX mode that Q6 drain voltage should be low, less than 1 V, while in TX mode it should be quite high, at least 90V DC.

73,
Mike, K8CN