[Elecraft] KPA100 bringup problem: only 1-W of output

[Brian Machesney]

Everything went smoothly through build and test until p. 47, "Transmit
Tests." I'm now going through the forest of DC checks, but I'm hoping
that someone among the august group of reflector-watchers can help me
understand what's happening, particularly since the "factory gurus" are
enjoying a well-deserved rest.

When I connect the KPA100 to a dummy load and enter TUNE mode at
0.1-10-W, everything looks good. When I increase the power to 11-W or
above, the output power indicated by the K2 is only 1-W (SWR=1.0). I
don't have an external wattmeter, but when I connect the rig to an
antenna the S-meter indication in a second receiver is consistent with
this behavior.

I'm using an Astron SS-25 supply. A digital multimeter placed in series
with the high-current supply leads indicates 520-mA in receive with PA
ON. In transmit it shows 1.75-A at 10-W power setting and 5.7-A at any
power setting of 11-W or higher. The K2's internal ammeter also shows
1.75-A at 10-W, but only 4.8-A at 11-W or above. From my reading of the
KPA100 manual, I thought the K2's internal ammeter reflected the current
into the 10-W amplifier stage; I didn't expect the K2's ammeter to show
more current after the KPA100 was engaged. Is this significant?

Can anyone more familiar with the KPA100 suggest where I should focus my
troubleshooting efforts? Thankfully, the base K2 still works the same as
before the KPA100 was installed, so I'm not totally QRT.

Brian K1LI
K2 #3070, K1 #252