My K2/100 has been working fine for a few years. Last weekend, I was
greeted by a HI CUR alarm when I first keyed down.
After some troubleshooting, here's what I've found:
If I remove the KPA100, the power control changes output power as
expected, and the power bar graph works to full scale.
With the KPA100 installed, and the power control below 10 W, the power
is 17 Watts regardless of the setting (0 to 10 W). If the power control
is set anywhere above 10 W, my meter is pegged at over 100 W out. I get
no indication on the bar graph at any setting.
I measured the V RFDET line at the DB9 on the KPA100 pin 7: in low power
mode (stuck at 17 W), the voltage is .310. In high power mode (pegged
over 100 W), the voltage is .410 V.
At first I suspected the DAC U8, but it works without the KPA100.
I'm guessing an input to the MCU is bad, causing it to drive the DAC U8
to full output.
A few questions:
For the base K2, it appears that the forward power calibration is fixed
in firmware (my settings don't match my calibrated power meter).
Where does the actual power control occur? I found "V PWR" coming out
of DAC U8 pin 2, but can't find it anywhere else on the schematic.
What are the inputs the MCU uses to drive the DAC?
All tests were done on 40 meters into a high quality 50 Ohm load. Other
bands have the same symptoms but I didn't bother to correct for the
coupling value for my CP1 coupler.
Since I can't vary power, I'm not sure what to expect for the Vforward
and Vreflected voltages in the KPA100 coupler circuit.
Thanks
Dave AA3EE
K2 s/n 5929
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