[Elecraft] K3 LPA failure, again

[Martin Sole]

Hi,

About 18 months ago both Q4 and Q5 the output devices in the LPA of my 
early K3 failed. I suspect this was partly my fault, trying to drive an 
amp known to take off and be generally unstable. I replaced the 
transistors and though at the time I had no hard and fast bias setting 
data the radio had worked fine until just now.

Seemingly out of the blue and having made several short transmissions it 
just coughed on 30m and died. No output of any sort from 0-110 watts and 
no indication that any power is being produced anywhere. And unlike last 
time there is no output at the XVTR out socket either. I think I have 
this enabled correctly with XV1 on, XV1RF 144, XV1 IF 28 and the power 
set to L1.5. With the band set to 144 I would expect to see adjustable 
power up to 1.5dBm at the XVTR out socket but nothing doing on the 
direct input of my LP100A.

Is this a known issue?

I did measure the fets. Several hundred ohms drain to source and several 
kilohms gate to source in circuit. 13.8 volts on the drains and a couple 
of volts bias when keyed. So it seem more like a lack of RF drive.

Where next?

Martin, HS0ZED