[Elecraft] [K2] KPA100 Troubleshooting - SWR high on low bands, Loss of power control

[Bill Coleman]

My KPA100 has been giving good service for nine and a half years. Back in July, it was giving me an INFO 080 issue, which I tracked down to a defective U6 - EL5146C on the KPA100. I've successfully replaced this chip, and now the KPA100 is responding.

Because of the part replacements, I have gone through the KPA100 alignment steps. The first indication of a problem was during the SWR Bridge Null Adjustment. While I could get a clear null, the display never showed anything less than 1.1 SWR on 40m.

Next the Power Calibration. This went fine as well, but when I checked the SWR on all the bands, I received a 1.8 SWR on 80m, and 2.6 on 160m. The highest bands gave a 1.0 indication, but most of the others were 1.1, just like 40m.

I double-checked my dummy load with my external watt meter. It appears they are 1.0 on all bands.

Doing some full-power tests:

* 40m - K2 indicates about 70 watts (7 bars), but the external watt meter shows 100 watts
* 80/160m - K2 indicates about 50 watts (5 bars), and sometimes I get a Hi Cur warning. The external watt meter shows 100 watts, or perhaps a little more.

Something is obviously wrong with the power measurement circuits here. Any suggestions as to what I should do to troubleshoot this further?