K3 repair - deafness after HI RFI warning

7 October 2015 | Comments

While operating at GB15NH, we managed to let the magic blue smoke out of two radios: Gavin M1BXF's IC-756ProIII, and my Elecraft K3.

The cause was entirely self-inflicted: our 20m and 17m antennas were probably 1m apart, and we didn't have a 17m band-pass filter to hand. We survived a day like this, but on the second day, the beams ended up facing each other, and this proved too much. The ProIII let out some smoke. We swapped it for the K3, which showed the "HI RFI" warning, then went suspiciously deaf.

Symptoms were:

Very deaf on main RX. Strongest signals in CQWW RTTY were S2.
Sub RX also deaf when sharing antenna with main RX.
RX antenna out was OK when fed into another rig.
Sub RX OK when using Aux RF antenna socket.

A bit of searching online pointed to D25, a double PIN diode. Iain M0PCB also reported problems with D5 on the KXV3A board.

Inspecting D25 (on the bottom of the RF board, near the LPA) showed it looking a bit supicious, and trying to remove it to test led to it disintegrating:

Original faulty D25

D25 is a BAR 64-05 PIN diode, and costs all of £0.40 from Mouser - plus a £12 delivery charge for small orders! I ordered 10, to give me plenty of spares if it happens again...

The new part installed:

New D25

Everything sprung back into life, with a -40dBm test signal from the Rigol DSA815's tracking generator lighting up the S-meter to 9+50dB, a much more reasonable value.