[Elecraft] KPA/100 displays wrong PS current (much lower)

[Ioannis Kassotakis]

Just finished building the KPA-100 for my S/N 2102 K2 (MCU v. 2.03D, KPA
1.06)
The K2/100 does not display the correct 13.8 V power supply current (by
taping Display) when it switches to HI POWER (>10 Watts).
I used a DMM in series to accurately measure the PS supplied current while
checking the K2 display at several power settings . Later, I also measured
the KPA TP1 voltage which is the I sense input to the KPA-100 processor.
For several power settings I got:
PWR (Watts) - PS Current (DMM) Amps - K2 Current Display Amps - KPA/100 TP1
(mV)
RX-0.4 - 0.44 - 0 <x-apple-data-detectors://0>
1.0- 1.72- 1.76 -0
5.0 - 3.3-3.3 - 0
10- 3.8 - 3.8 - 0
15- 4.5 - 1.01 - Not measured
20- 5.4 - 1.02 - 100
40 - 7.0 - 1.20 - 250
60 - 8.5 - 1.28 -380
80 - 9.5 - 1.41 - 500
100 - 10.3 - 1.48 - 580
111 - 10.8 - 1.54 - N/A
The measurements were done at 40 m (7.100) at CW to a dummy load through
KAT-100.

It seems to work fine a LO PWR (<11 Watts) but appears to have a scaling
issue, when the PA switches On to HI PWR mode.
According to the schem (p.61) I Sense is supposed to vary 0-5 V for 0-32 A,
so the TP1 figures seem to be rather low.
Is this a known issue? Is it possible that I have a failed U7 or Q5 ?

Thanks!

Ioannis


-- 
Ioannis Kassotakis