K2 signal tracing progress and questions arising

Posted by Paul Fletcher on Nov 10, 2009; 10:00pm
URL: http://elecraft.85.s1.nabble.com/K2-signal-tracing-progress-and-questions-arising-tp3982841.html

Hi all,

Progressing with fault finding the K2 and there are some immediate apparent issues. Firstly there is a lot of loss through the low pass filters on receive (on 30m at least) - 3dB when the actual loss should be negligible. That's obviously one place I need to look. However (weird one this) the output measured from the bandpass filters is higher than the input. On my scope I'm measuring 78mV pk to pk on the input and 135mV pk to pk on the output of the filters at the junction of D6 and D7 which is clearly not what is expected (unless this particular K2 has somehow broken the laws of physics). I'm wondering if it's possible that something in the transmit chain is active? I have checked the 8T and 8R voltages and they are OK. Downstream of D6 losses seem comparable with the Signal tracing checklist until I get to the composite mixer where everything takes a dive down (another area to check).

Any thoughts on the bandpass filter issue?

Cheers,
Paul.