[Elecraft] K60XV with KAT2 ALC problem

[Gregory P. Daly]

Here's a fun one..... I drive my transverters with 0dBm (1.00 mW) from
the K60XV..... no trouble, nice, stable power control..... I add a KAT2
and a battery (VHF isn't everything). If I set the transverter drive to
anything from .01 mW to around .40 mW things are normal, if I set the
drive to the transverter above about .70. mW, the output of the
transverter goes onto saturation (about 25 watts, Bird 43 with "50D"
slug). I measured the transverter drive level with my HP435A and 8481A
power sensor (valid calibration stickers on both, no flames about crappy
power meters).... and it's making 1.35 mW. It continues to make 1.35 mW
until I turn the indicated drive level down to about .7 mW when it gets
a handle on the power level and makes 0.630 mW.

So I pry the lit off the radio.

With the tuner plugged in, the ALC voltage, on pin 6 of J13 on the
K60XV, varies from 0.820V at minimum power to 2.971V (Fluke 8060A with
current calibration sticker, all the digits are correct) when it stops
going up, at .70 mW indicated, it looses ALC control.

With the tuner unplugged, it seems happy, ALC runs from 0.811 to 3.505V
when it's claiming to be making 1 mW (it really only makes 0.820 mW but
I can live with 0.8 dB low. I'll work on calibration later).

I looked at the tuner, R6 (47 ohms) is present and correct. R6
"isolates" the ALC buss from the low output impedance of the LM358 that
makes the forward power indication on the buss.

On the K60XV board, the +6V VDD supply is present and correct (6.091V)
at all times. When the transverter function is selected, pin 10 of the
PIC, the "6LP" signal goes to very nearly VDD, 5.994V, if the tuner is
unplugged. (not bad for a very small MOSFET in the PIC)

With the tuner plugged in, The 6LP signal drops to 4.973V, and the
output of U2 at pin 1 drops to 3.96V, causing the emitter of Q2 to drop
to 2.97V. I think Q2 is good, in "normal" operation, it makes 3.491V on
the emitter (ALC buss) with 4.031V on the base (540 mV VBE) I think it's
running out of collector voltage, and the 1V VBE is because it's
saturated.

Does this configuration work for anybody else? Is the PIC on the K60XV
able to source enough current to "pull" the ALC buss far enough when the
tuner is present? I don't have the PA, is the PA ALC circuit the same,
and will K60XV work with a PA present? Is my PIC bad? I haven't
downloaded the spec for the 16C621A from Microchip yet, how much current
is it supposed to make?

Have I made another gross blunder?

73 DE WB7RSG

Greg.